Pagewidth printhead having sealed inkjet actuators

ABSTRACT

An inkjet printhead is provided having an elongate ink supply channel defined within a substrate and a plurality of inkjet nozzles arranged on the substrate to extend across a pagewidth. Each nozzle incorporates an actuator of a conductive heater, a paddle and an arm interconnecting the heater and paddle, and an ink ejection chamber having a first wall in which a first aperture for ink ejection is defined, a second wall in which a second aperture is defined through which the arm of the actuator passes so that the heater is outside the chamber and the paddle is inside the chamber, and a third wall in which a third aperture is defined through which ink from the ink supply channel is communicated. The arm of each actuator incorporates a protruding shield configured to restrict the flow of ink through the second aperture.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.11,478,598 filed on Jul. 3, 2006, now issued as Pat. No. 7,182,437,which is a continuation of U.S. application Ser. No. 11/144,757 filedJun. 6, 2005, now issued as U.S. Pat. No. 7,080,895, which is acontinuation of U.S. application Ser. No 09/807,297 filed Aug. 13, 2001,now issued as U.S. Pat. No. 6,902,255, which is a 371 of PCT/AU99/00894filed Oct. 15, 1999, all of which is herein incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to the construction of micro-electromechanical devices such as ink jet printers.

BACKGROUND OF THE INVENTION

In international patent application PCT/AU98/00550, the presentapplicant has proposed an ink jet printing device which utilisesmicro-electro mechanical (mems) processing techniques in theconstruction of a print head driven by thermal bend actuator devices forthe ejection of fluid such as ink from an array of nozzle chambers.

Devices of this type have a number of limitations and problems.

It is an object of the present invention to provide various aspects ofan inkjet printing device which overcomes or at least ameliorates one ofor more of the disadvantages of the prior art or which at least offers auseful alternative thereto.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention, there isprovided an inkjet printhead having a series of nozzles for the ejectionof ink wherein each said nozzle has a rim formed by the conformaldeposition of a rim material layer over a sacrificial layer and asubsequent planar etching of at least said rim material layer so as toform said nozzle rim.

The planar etching can comprise chemical—mechanical planarization of therim material layer and any associated sacrificial layers.

In accordance with a second aspect of the present invention, there isprovided an inkjet printhead comprising:

a plurality of nozzle chambers each having an ink ejection aperture inone wall thereof and an actuator interconnection aperture in a secondwall thereof;

a moveable ink ejection paddle located within the nozzle chamber andmoveable under the control of an external thermal actuator through saidactuator interconnection aperture for the ejection of ink out of saidink ejection aperture;

said external actuator being covered by a protective covering shellaround the operational portions of said actuator, spaced apart from saidactuator.

The protective covering shell can be formed simultaneously with theformation of other portions of the inkjet printing arrangement inparticular with the nozzle chamber walls.

The protective covering shell can be formed by deposition and etching ofa sacrificial material layer followed by deposition and etching of aninert material layer forming the covering shell.

The external actuator can comprise a thermal bend actuator.

In accordance with a third aspect of the present invention, thee isprovided a method of forming an inkjet printhead on a substrate saidmethod including:

providing a first substrate on which is formed electrical drivecircuitry made up of one or more interleaved layers of conductive,semi-conductive and non-conductive materials for the control of saidinkjet printhead;

forming on said substrate at least one nozzle chamber having an inkejection aperture in one wall thereof;

providing a moveable ink ejection paddle within said nozzle chamber,moveable under the control of an actuator for the ejection of ink out ofsaid ink ejection aperture;

and utilizing portions of at least one of said interleaved layers as asacrificial material layer in the formation of one or more of the groupcomprising said actuator and said ink ejection paddle.

The sacrificial material layer can comprise portions of a conductivelayer of the electrical drive circuitry. The electrical drive circuitrycan comprise a Complementary Metal Oxide (CMOS) process and thesacrificial material layer can comprise a CMOS metal layer.

The sacrificial material layer can be utilized in formulating theactuator. The actuator can comprise a thermal actuator. The actuator canbe located external to the nozzle chamber and can be interconnected tothe ink ejection paddle through an actuation interconnection apertureformed in a second wall of the nozzle chamber.

In accordance with a fourth aspect of the preset invention, there isprovided an inkjet printhead constructed by MEMS processing techniqueswith a plurality of ink ejection nozzles each having a nozzle chamber,an external thermal bend actuator having a proximal end anchored to asubstrate and a distal end connected to an ink ejection paddle withinsaid chamber;

wherein said external thermal bend actuator further comprises a seriesof layers and includes a planar conductive heating circuit layer whichincludes a first portion adjacent said proximal end forming a planarconductive heating circuit for heating said thermal bend actuator, and asecond portion extending into said ink ejection paddle, said secondportion being electrically isolated from said first portion by means ofa discontinuity in said planar conductive heating circuit layer, saiddiscontinuity being located external to said nozzle chamber.

The planar conductive heating circuit layer can comprise substantiallytitanium nitride. The conductive circuit preferably can include at leastone tapered portion adjacent the proximal end so as to increaseresistive heating adjacent the proximal end.

In accordance with a fifth speci of the present invention, there isprovided an inkjet printhead having a series of ink ejection nozzles forthe ejection of ink, each of said nozzles interconnecting a nozzlechamber with an external atmosphere, each said nozzle having a firstmeniscus rim around which an ink meniscus normally forms, and anextended ink flow prevention rim spaced outwardly from said firstmeniscus rim and substantially encircling said first meniscus rim,arranged to prevent the flow of ink across the surface of said inkjetprinthead.

The ink flow prevention rim can be substantially co-planar with thefirst meniscus rim and can be formed from the same material as the firstmeniscus rim.

The ink flow prevention rim and the first meniscus rim are preferablyformed utilizing chemical mechanical planarization.

The ink flow prevention rim and the first meniscus rim are preferablyformed from Titanium Nitride.

In accordance with a sixth aspect of the present invention, there isprovided a movable micromechanical device including a bend actuatoradapted to curve in a first bending direction and having a substantiallyplanar bottom surface, said bend actuator being formed on a planesubstrate on top of a number of deposited lower layers, wherein the bendactuator is formed by a plurality of steps including:

forming a series of structures in said deposited lower layers, saidseries of structures having a surface profile including a series ofelongate ribs running in a direction substantially transverse to saidfirst being direction.

The bend actuator can comprise a thermal bend actuator. The depositedlayers can include a conductive circuitry layer and can beinterconnected to the bend actuator for activation of the bend actuator.The bend actuator can be attached to a paddle member and actuated forthe ejection of ink from an ink ejection nozzle of an inkjet printhead.The deposited layer, located under the bend actuator can include a powertransistor for the control of operation of the bend actuator.

In accordance with a seventh aspect o the present invention, there isprovided a method of construction of an inkjet printhead having a largearray of inkjet nozzle arrangements said method comprising:

defining a single inkjet nozzle arrangement for the ejection of ink froma single nozzle; and

utilizing a series of translations and rotations of said single inkjetnozzle arrangement to form all the inkjet nozzles of said inkjet printhead;

said utilizing step including:

initially forming a plurality of nozzles in a pod;

forming a group of pods, each group corresponding to a different coloredink dispensed from said printhead;

forming a plurality of said groups of pods into a firing group;

combining firing groups forming a segment of said printhead;

forming each segment together to form said printhead.

The inkjet nozzle arrangements can include a series of layers depositedand etch utilizing a mask. The layers can include conductive layerswhich are preferably etched utilizing the mask so as to form a series ofconductive interconnections. The conductive interconnects can includeinterconnects with adjacent versions of the inkjet nozzle arrangementwhich can comprise translated and/or rotated copies of the inkjet nozzlearrangement.

In accordance with an eighth aspect of the present invention, there isprovided a method of operation of a fluid ejection printhead within apredetermined thermal range so as to print an image, said printheadincluding a series of thermal actuators operated to eject fluid fromsaid printhead, said method comprising the steps of:

-   -   (a) sensing the printhead temperature of said printhead to        determine if said printhead temperature is below a predetermined        threshold,    -   (b) if said printhead temperature is below said predetermined        threshold, performing a preheating step of heating said        printhead so that it is above said predetermined threshold,    -   (c) controlling said preheating step such that said thermal        actuators are heated to an extent insufficient to cause the        ejection of fluid from said printhead; and    -   (d) utilizing said printhead to print said image.

The step (a) can further preferably include the steps of: (aa) initiallysensing an ambient temperature surrounding the printhead; (ab) settingthe predetermined threshold to be the ambient temperature plus apredetermined operational factor amount, the operational factor amountbeing dependant on the ambient temperature.

The method can further comprise the step of: (d) monitoring theprinthead temperature whilst printing the image and where thetemperature falls below the predetermined threshold, reheating theprinthead so that it can be above the predetermined threshold.

The step (b) can comprise constantly monitoring the printheadtemperature whilst heating the printhead.

The step (c) further can comprise applying a series of short electricalpulses so the thermal actuators, each being insufficient to cause theejection of fluid from the printhead.

In accordance with an additional aspect of the eighth aspect of thepresent invention, there is provided a fluid ejection device comprising:

an array of nozzles formed on a substrate and adapted to eject ink ondemand by means of a series of ink ejection thermal actuators actuatedby an actuator activation unit attached to said ink ejection actuatorsfor activation thereof;

at least one temperature sensor attached to said substrate for sensingthe temperature of said substrate; and

a temperature sensor unit;

wherein before a fluid ejection operation is begun said temperaturesensor unit utilizes said at least one temperature sensor to sense acurrent temperature of said substrate, and if said temperature is belowa predetermined limit, to output a preheat activation signal to saidactuator activation unit, whereupon said actuator activation unitactivates said ink ejection thermal actuators to an extent sufficient toheat said substrate, while being insufficient for the ejection of inkfrom said array.

The at least one temperature sensor can comprise a series of spacedapart temperature sensors formed on the print head.

The array of nozzles are preferably divided into a series of spacedapart segments with at least one temperature sensor per segment.

In accordance with a ninth aspect of the present invention, there isprovided an ink supply arrangement for supplying ink to the printingarrangement of a portable printer, said ink supply arrangementincluding:

an ink supply unit including at least one storage chamber for holdingink for supply to said printing arrangement, said ink supply unitincluding a series of spaced apart baffles configured so as to reducethe acceleration of the ink within the unit as may be induced bymovement of the portable printer, whilst allowing for flows of ink tothe printing arrangement in response to active demand therefrom.

Preferably, the ink printing arrangement is in the form of a printheadwhich is connected directly to an ink supply arrangement in the form ofan ink supply unit having an ink distribution manifold that supplies inkvia a plurality of outlets to corresponding ink supply passages formedon the printhead.

In the preferred form, the printhead is an elongate pagewidth printheadchip and the baffles in the ink supply are configured to reduceacceleration of the ink in a direction along the longitudinal extent ofthe printhead and corresponding ink supply unit. Preferably, the inksupply unit has a series of storage chambers for holding separate colorinks.

Preferably, the ink storage chamber or chambers are constructed from twoor more interconnecting molded components.

In accordance with a tenth aspect of the present invention, there isprovided a power distribution arrangement for an elongate inkjetprinthead of a kind having a plurality of longitudinally spaced voltagesupply points, said power distribution arrangement including:

two or more elongate low resistance power supply busbars; and

interconnect means to connect a selected plurality of said voltagesupply points to said busbars.

Preferably the busbars are disposed to extend parallel to said printheadand said interconnect means provide interconnections extending generallytransversely therebetween.

In a preferred form the interconnect means is in the form of a tapeautomated bonded film (TAB film).

Desirably the TAB film electrically connects with said busbars by meansof correspondingly sized noble metal deposited strips formed on said TABfilm.

Preferably the interconnect means also includes a plurality of controllines for connection to selected other of said voltage supply points onsaid printhead.

The unit can be detachable from the power supply and the external seriesof control lines. The conductive rails can comprise two mechanicallystiff conductive bars.

In accordance with an eleventh aspect of the invention there is providedan ink supply unit for supplying a printhead containing an array of inkejection nozzles, said supply unit comprising:

a first member formed having dimensions refined to a first accuracy andhaving a first cavity defined therein;

a second member in the form of an ink distribution manifold having asecond cavity defined therein, said second cavity being adapted for theinserted of a printhead;

said second member being configured to engage said first cavity in saidfirst member so as to define one or more chambers for the supply of inkto ink supply passages formed in said printhead;

said second member being formed having dimensions refined to a secondaccuracy which is higher than said first accuracy.

Preferably, the first and second members are configured to togetherdefine a series of ink storage chambers, desirably suitable for storingdifferent colored inks.

In the preferred form the second member defines a series of discrete inkoutlets that are adapted to provide ink to ink supply passages in theprinthead that are adapted to supply ink to grouped sets of ink ejectionnozzles.

Preferably, the second member has overall external dimensions that aresubstantially smaller than those of the first member.

In accordance with an additional aspect of the eleventh aspect of thepresent invention, there is provided an ink supply unit for supplying amultiple color pagewidth ink supply printhead, comprising: a firstelongated member containing a series of chambers for the storage ofseparate color inks and formed having dimensions refined to a firstaccuracy and having a first elongated cavity defined therein; a secondelongated member including a series of wall elements and a secondelongated cavity defined therein, the second elongated cavity beingadapted for the insertion of a page width ink jet printhead, the wallelements mating with corresponding elements of the first elongatedmember to complete the formation of the series of chambers for thesupply of ink to a series of slots formed in the back of the printheadwhen inserted in the second elongated cavity, wherein the secondelongate member is formed having dimensions refined to a second accuracywhich is higher then the first accuracy.

A screen for filtering portions of the ink supply flowing through to theprinthead is preferably provided, optionally as part of the secondmember.

The first elongated member and/or the second elongated member caninclude a series of baffles for reducing the acceleration of the inkwithin the ink supply unit.

In accordance with a twelfth aspect of the present invention, there isprovided a method of interconnecting a printhead containing an array ofink ejection nozzles to an ink distribution manifold, said methodcomprising:

attaching said printhead to said ink distribution manifold utilizing aresilient adhesive adapted to be elastically deformed with anydeflections of the ink distribution manifold.

In accordance with an additional aspect of the twelfth aspect of theinvention there is provided a printhead and ink distribution manifoldassembly wherein said printhead is attached to said ink distributionmanifold by means of a resilient adhesive adapted to be elasticallydeformed with any deflections of the ink distribution manifold.

In the preferred form the printhead is an elongate pagewidth printheadchip and the ink distribution manifold forms part of an ink supply unit.Desirably the ink supply unit comprises:

a first elongated member containing a series of chambers for the storageof separate color inks and having a first elongated cavity definedtherein;

a second elongated member including a series of wall elements and asecond elongated cavity defined therein, said second elongated cavitybeing adapted for the insertion of a page width ink jet printhead, saidwall elements mating with corresponding elements of said first elongatedmember to complete the formation of said series of chambers for thesupply of ink to a series of slots formed in the back of said printheadwhen inserted in said second elongated cavity,

wherein said second elongated member is interconnected to said firstelongated member utilizing to a resilient adhesive adapted to beelastically deformed with any bending of said ink supply unit.

The printhead chip can be attached to the ink supply unit along thesides and along a back surface thereof.

In accordance with a thirteenth aspect of the present invention, thereis provided an inkjet printhead comprising:

a plurality of nozzle chambers, each having a nozzle aperture defined inone wall thereof for the ejection of ink out of said aperture;

an ink supply channel interconnected with said nozzle chamber;

a paddle moveable within the nozzle chamber by an actuator and operableto eject ink from said nozzle chamber, said paddle having a projectingpart which, upon operation of said actuator is caused to move towardssaid nozzle aperture.

Preferably, the projecting part, upon activation of the actuator, movesthrough the plane of the aperture and can be located concentrically withthe nozzle aperture.

The liquid ejection aperture can be formed utilizing the deposition andetching of a series of layers and the projecting part can comprise ahollow cylindrical column.

The hollow cylindrical column preferably can include an end adjacent theaperture which can be chemically mechanically planarized during theformation of the aperture.

The actuator can comprise a thermal bend actuator conductively heated soas to cause movement of the paddle.

The projecting part can be located substantially centrally on thepaddle.

In accordance with an additional aspect of the thirteenth aspect of thepresent invention, there is provided in an inkjet printhead having atleast one chamber from which liquid is ejected from a nozzle apertureinterconnected with said chamber by means of movement of a liquidejection paddle, a method of improving the operational characteristicsof said printhead comprising the steps of:

locating a projecting part on said moveable paddle, said projecting partundergoing movement towards said nozzle aperture upon activation of saidliquid ejection paddle to eject fluid.

The projection part preferably can include an end portion which movesthrough the plane of an outer rim of the aperture upon activation of theliquid ejection paddle.

In accordance with a fourteenth aspect of the present invention, thereis provided an inkjet printhead apparatus comprising:

a plurality of nozzle chambers each having a nozzle aperture defined inone wall thereof for the ejection of ink out of said chamber and asecond aperture for the insertion of an actuator mechanism;

an ink supply channel interconnected with said nozzle chamber;

a paddle moveable by an actuator operable to eject ink from said nozzlechamber, said actuator including:

a first portion located externally of said nozzle chamber and

a second portion located internally of said nozzle chamber, supportingsaid paddle;

an interconnecting portion interconnecting said first portion and saidsecond portion through said second aperture, said interconnectingportion further including a protruding shield formed adjacent saidsecond aperture and positioned so as to restrict the flow of fluidthrough said second aperture.

The shield can comprise a hydrophobic surface. The interconnectingportion typically moves in an upwardly defined direction towards theliquid ejection aperture, and the shield can be formed on a top surfaceof the portion. The actuator preferably can include a thermal expansionactuator located in the first portion.

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms which may fall within the scope of thepresent invention, preferred forms of the invention will now bedescribed, by way of example only, with reference to the accompanyingdrawings in which:

FIG. 1. illustrates schematically a single ink jet nozzle in a quiescentposition;

FIG. 2 illustrates schematically a single ink jet nozzle in a firingposition;

FIG. 3 illustrates schematically a single ink jet nozzle in a refillingposition;

FIG. 4 illustrates a bi-layer cooling process;

FIG. 5 illustrates a single layer cooling process;

FIG. 6 is a top view of an aligned nozzle;

FIG. 7 is a sectional view of an aligned nozzle;

FIG. 8 is a top view of an aligned nozzle;

FIG. 9 is a sectional view of an aligned nozzle;

FIG. 10 is a sectional view of a process on constructing an ink jetnozzle;

FIG. 11 is a sectional view of a process on constructing an ink jetnozzle after Chemical Mechanical Planarization;

FIG. 12 illustrates the steps involved in the preferred embodiment inpreheating the ink;

FIG. 13 illustrates the normal printing clocking cycle;

FIG. 14 illustrates the utilization of a preheating cycle;

FIG. 15 illustrates a graph of likely print head operation temperature;

FIG. 16 illustrates a graph of likely print head operation temperature;

FIG. 17 illustrates one form of driving a print head for preheating;

FIG. 18 illustrates a sectional view of a portion of an initial wafer onwhich an ink jet nozzle structure is to be formed;

FIG. 19 illustrates the mask for N-well processing;

FIG. 20 illustrates a sectional view of a portion of the wafer afterN-well processing;

FIG. 21 illustrates a side perspective view partly in section of asingle nozzle after N-well processing;

FIG. 22 illustrates the active channel mask;

FIG. 23 illustrates a sectional view of the field oxide;

FIG. 24 illustrates a side perspective view partly in section of asingle nozzle after field oxide deposition;

FIG. 25 illustrates the poly mask;

FIG. 26 illustrates a sectional view of the deposited poly;

FIG. 27 illustrates a side perspective view partly in section of asingle nozzle after poly deposition;

FIG. 28 illustrates the n+ mask;

FIG. 29 illustrates a sectional view of the n+ implant;

FIG. 30 illustrates a side perspective view partly in section of asingle nozzle after n+ implant;

FIG. 31 illustrates the p+ mask;

FIG. 32 illustrates a sectional view showing the effect of the p+implant;

FIG. 33 illustrates a side perspective view partly in section of asingle nozzle after p+ implant;

FIG. 34 illustrates the contacts mask;

FIG. 35 illustrates a sectional view showing the effects of depositingILD 1 and etching contact vias;

FIG. 36 illustrates a side perspective view partly in section of asingle nozzle after depositing ILD 1 and etching contact vias;

FIG. 37 illustrates the Metal 1 mask,

FIG. 38 illustrates a sectional view showing the effect of the metaldeposition of the Metal 1 layer;

FIG. 39 illustrates a side perspective view partly in section of asingle nozzle after metal 1 deposition;

FIG. 40 illustrates the Via 1 mask;

FIG. 41 illustrates a sectional view showing the effects of depositingILD 2 and etching contact vias;

FIG. 42 illustrates the Metal 2 mask;

FIG. 43 illustrates a sectional view showing the effects of depositingthe Metal 2 layer;

FIG. 44 illustrates a side perspective view partly in section of asingle nozzle after metal 2 deposition;

FIG. 45 illustrates the Via 2 mask;

FIG. 46 illustrates a sectional view showing the effects of depositingILD 3 and etching contact vias;

FIG. 47 illustrates the Metal 3 mask;

FIG. 48 illustrates a sectional view showing the effects of depositingthe Metal 3 layer;

FIG. 49 illustrates a side perspective view partly in section of asingle nozzle after metal 3 deposition;

FIG. 50 illustrates the Via 3 mask;

FIG. 51 illustrates a sectional view showing the effects of depositingpassivation oxide and nitride and etching vias;

FIG. 52 illustrates a side perspective view partly in section of asingle nozzle after depositing passivation oxide and nitride and etchingvias;

FIG. 53 illustrates the heater mask;

FIG. 54 illustrates a sectional view showing the effect of depositingthe heater titanium nitride layer;

FIG. 55 illustrates a side perspective view partly in section of asingle nozzle after depositing the heater titanium nitride layer;

FIG. 56 illustrates the actuator/bend compensator mask;

FIG. 57 illustrates a sectional view showing the effect of depositingthe actuator glass and bend compensator titanium nitride after etching;

FIG. 58 illustrates a side perspective view partly in section of asingle nozzle after depositing and etching the actuator glass and bendcompensator titanium nitride layers;

FIG. 59 illustrates the nozzle mask;

FIG. 60 illustrates a sectional view showing the effect of thedepositing of the sacrificial layer and etching the nozzles.

FIG. 61 illustrates a side perspective view partly in section of asingle nozzle after depositing and initial etching the sacrificiallayer;

FIG. 62 illustrates the nozzle chamber mask;

FIG. 63 illustrates a sectional view showing the etched chambers in thesacrificial layer;

FIG. 64 illustrates a side perspective view partly in section of asingle nozzle after further etching of the sacrificial layer;

FIG. 65 illustrates a sectional view showing the deposited layer of thenozzle chamber walls;

FIG. 66 illustrates a side perspective view partly in section of asingle nozzle after further deposition of the nozzle chamber walls;

FIG. 67 illustrates a sectional view showing the process of creatingself aligned nozzles using Chemical Mechanical Planarization (CMP);

FIG. 68 illustrates a side perspective view partly in section of asingle nozzle after CMP of the nozzle chamber walls;

FIG. 69 illustrates a sectional view showing the nozzle mounted on awafer blank;

FIG. 70 illustrates the back etch inlet mask;

FIG. 71 illustrates a sectional view showing the etching away of thesacrificial layers;

FIG. 72 illustrates a side perspective view partly in section of asingle nozzle after etching away of the sacrificial layers;

FIG. 73 illustrates a side perspective view partly in section of asingle nozzle after etching away of the sacrificial layers taken along adifferent section line;

FIG. 74 illustrates a sectional view showing a nozzle filled with ink;

FIG. 75 illustrates a side perspective view partly in section of asingle nozzle ejecting ink;

FIG. 76 illustrates a schematic of the control logic for a singlenozzle;

FIG. 77 illustrates a CMOS implementation of the control logic of asingle nozzle;

FIG. 78 illustrates a legend or key of the various layers utilized inthe described CMOS/MEMS implementation;

FIG. 79 illustrates the CMOS levels up to the poly level;

FIG. 80 illustrates the CMOS levels up to the metal 1 level;

FIG. 81 illustrates the CMOS levels up to the metal 2 level;

FIG. 82 illustrates the CMOS levels up to the metal 3 level;

FIG. 83 illustrates the CMOS and MEMS levels up to the MEMS heaterlevel;

FIG. 84 illustrates the Actuator Shroud Level;

FIG. 85 illustrates a side perspective partly in section of a portion ofan ink jet head;

FIG. 86 illustrates an enlarged view of a side perspective partly insection of a portion of an ink jet head;

FIG. 87 illustrates a number of layers formed in the construction of aseries of actuators;

FIG. 88 illustrates a portion of the back surface of a wafer showing thethrough wafer ink supply channels;

FIG. 89 illustrates the arrangement of segments in a print head;

FIG. 90 illustrates schematically a single pod numbered by firing order;

FIG. 91 illustrates schematically a single pod numbered by logicalorder;

FIG. 92 illustrates schematically a single tripod containing one pod ofeach color;

FIG. 93 illustrates schematically a single podgroup containing 10tripods;

FIG. 94 illustrates schematically, the relationship between segments,firegroups and tripods;

FIG. 95 illustrates clocking for AEnable and BEnable during a typicalprint cycle;

FIG. 96 illustrates an exploded perspective view of the incorporation ofa print head into an ink channel molding support structure;

FIG. 97 illustrates a side perspective view partly in section of the inkchannel molding support structure;

FIG. 98 illustrates a side perspective view partly in section of a printroll unit, print head and platen; and

FIG. 99 illustrates a side perspective view of a print roll unit, printhead and platen;

FIG. 100 illustrates a side exploded perspective view of a print rollunit, print head and platen;

FIG. 101 is an enlarged perspective part view illustrating theattachment of a print head to an ink distribution manifold as shown inFIGS. 96 and 97;

FIG. 102 illustrates an opened out plan view of the outermost side ofthe tape automated bonded film shown in FIG. 97; and

FIG. 103 illustrates the reverse side of the opened out tape automatedbonded film shown in FIG. 102.

FIG. 104-106 illustrates schematically the operational principles of thepreferred embodiments;

FIG. 107 is a side perspective view, partly in section, of a singlenozzle arrangement of the preferred embodiments;

FIG. 108 illustrates a side perspective of a single nozzle including theshroud arrangement; and

FIG. 109-111 illustrates the principles of chemical, mechanicalplanarization utilized in the formation of the preferred embodiment.

DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS

The preferred embodiment is a 1600 dpi modular monolithic print headsuitable for incorporation into a wide variety of page width printersand in print-on-demand camera systems. The print head is fabricated bymeans of Micro-Electro-Mechanical-Systems (MEMS) technology, whichrefers to mechanical systems built on the micron scale, usually usingtechnologies developed for integrated circuit fabrication.

As more than 50,000 nozzles are required for a 1600 dpi A4 photographicquality page width printer, integration of the drive electronics on thesame chip as the print head is essential to achieve low cost.Integration allows the number of external connections to the print headto be reduced from around 50,000 to around 100. To provide the driveelectronics, the preferred embodiment integrates CMOS logic and drivetransistors on the same wafer as the MEMS nozzles. MEMS has severalmajor advantages over other manufacturing techniques:

mechanical devices can be built with dimensions and accuracy on themicron scale;

millions of mechanical devices can be made simultaneously, on the samesilicon wafer; and

the mechanical devices can incorporate electronics.

The term “IJ46 print head” is used herein to identify print heads madeaccording to the preferred embodiment of this invention.

Operating Principle

The preferred embodiment relies on the utilization of a thermallyactuated lever arm which is utilized for the ejection of ink. The nozzlechamber from which ink ejection occurs includes a thin nozzle rim aroundwhich a surface meniscus is formed. A nozzle rim is formed utilizing aself aligning deposition mechanism. The preferred embodiments alsoincludes the advantageous feature of a flood prevention rim around theink ejection nozzle.

Turning initially to FIG. 1 to FIG. 3, there will be now initiallyexplained the operation of principles of the ink jet print head of thepreferred embodiment. In FIG. 1, there is illustrated a single nozzlearrangement 1 which includes a nozzle chamber 2 which is supplied via anink supply channel 3 so as to form a meniscus 4 around a nozzle rim 5. Athermal actuator mechanism 6 is provided and includes an end paddle 7which can be a circular form. The paddle 7 is attached to an actuatorarm 8 which pivots at a post 9. The actuator arm 8 includes two layers10, 11 which are formed from a conductive material having a high degreeof stiffness, such as titanium nitride. The bottom layer 10 forms aconductive circuit interconnected to post 9 and further includes athinned portion near the end post 9. Hence, upon passing a currentthrough the bottom layer 10, the bottom layer is heated in the areaadjacent the post 9. Without the heating, the two layers 10, 11 are inthermal balance with one another. The heating of the bottom layer 10causes the overall actuator mechanism 6 to bend generally upwards andhence paddle 7 as indicated in FIG. 2 undergoes a rapid upward movement.The rapid upward movement results in an increase in pressure around therim 5 which results in a general expansion of the meniscus 4 as inkflows outside the chamber. The conduction to the bottom layer 10 is thenturned off and the actuator arm 6, as illustrated in FIG. 3 begins toreturn to its quiescent position. The return results in a movement ofthe paddle 7 in a downward direction. This in turn results in a generalsucking back of the ink around the nozzle 5. The forward momentum of theink outside the nozzle in addition to the backward momentum of the inkwithin the nozzle chamber results in a drop 14 being formed as a resultof a necking and breaking of the meniscus 4. Subsequently, due tosurface tension effects across the meniscus 4, ink is drawn into thenozzle chamber 2 from the ink supply channel 3.

The operation of the preferred embodiment has a number of significantfeatures. Firstly, there is the aforementioned balancing of the layer10, 11. The utilization of a second layer 11 allows for more efficientthermal operation of the actuator device 6. Further, the two layeroperation ensures thermal stresses are not a problem upon cooling duringmanufacture, thereby reducing the likelihood of peeling duringfabrication. This is illustrated in FIG. 4 and FIG. 5. In FIG. 4, thereis shown the process of cooling off a thermal actuator arm having twobalanced material layers 20, 21 surrounding a central material layer 22.The cooling process affects each of the conductive layers 20, 21 equallyresulting in a stable configuration. In FIG. 5, a thermal actuator armhaving only one conductive layer 20 as shown. Upon cooling aftermanufacture, the upper layer 20 is going to bend with respect to thecentral layer 22. This is likely to cause problems due to theinstability of the final arrangement and variations and thickness ofvarious layers which will result in different degrees of bending.

Further, the arrangement described with reference to FIGS. 1 to 3includes an ink jet spreading prevention rim 25 (FIG. 1) which isconstructed so as to provide for a pit 26 around the nozzle rim 5. Anyink which should flow outside of the nozzle rim 5 is generally caughtwithin the pit 26 around the rim and thereby prevented from flowingacross the surface of the ink jet print head and influencing operation.This arrangement can be clearly seen in FIG. 11.

Further, the nozzle rim 5 and ink spread prevention rim 25 are formedvia a unique chemical mechanical planarization technique. Thisarrangement can be understood by reference to FIG. 6 to FIG. 9. Ideally,an ink ejection nozzle rim is highly symmetrical in form as illustratedat 30 in FIG. 6. The utilization of a thin highly regular rim isdesirable when it is time to eject ink. For example, in FIG. 7 there isillustrated a drop being ejected from a rim during the necking andbreaking process. The necking and breaking process is a high sensitiveone, complex chaotic forces being involved. Should standard lithographybe utilized to form the nozzle rim, it is likely that the regularity orsymmetry of the rim can only be guaranteed to within a certain degree ofvariation in accordance with the lithographic process utilized. This mayresult in a variation of the rim as illustrated at 35 in FIG. 8. The rimvariation leads to a non-symmetrical rim 35 as illustrated in FIG. 8.This variation is likely to cause problems when forming a droplet. Theproblem is illustrated in FIG. 9 wherein the meniscus 36 creeps alongthe surface 37 where the rim is bulging to a greater width. This resultsin an ejected drop likely to have a higher variance in direction ofejection.

In the preferred embodiment, to overcome this problem, a self aligningchemical mechanical planarization (CMP) technique is utilized. Asimplified illustration of this technique will now be discussed withreference to FIG. 10. In FIG. 10, there is illustrated a siliconsubstrate 40 upon which is deposited a first sacrificial layer 41 and athin nozzle layer 42 shown in exaggerated form. The sacrificial layer isfirst deposited and etched so as to form a “blank” for the nozzle layer42 which is deposited over all surfaces conformally. In an alternativemanufacturing process, a further sacrificial material layer can bedeposited on top of the nozzle layer 42.

Next, the critical step is to chemically mechanically planarize thenozzle layer and sacrificial layers down to a first level eg. 44. Thechemical mechanical planarization process acts to effectively “chop off”the top layers down to level 44. Through the utilization of conformaldeposition, a regular rim is produced. The result, after chemicalmechanical planarization, is illustrated schematically in FIG. 11.

The description of the preferred embodiments will now proceed by firstdescribing an ink jet preheating step preferably utilized in the IJ46device.

Ink Preheating

In the preferred embodiment, an ink preheating step is utilized so as tobring the temperature of the print head arrangement to be within apredetermined bound. The steps utilized are illustrated at 101 in FIG.12. Initially, the decision to initiate a printing run is made at 102.Before any printing has begun, the current temperature of the print headis sensed to determine whether it is above a predetermined threshold. Ifthe heated temperature is too low, a preheat cycle 104 is applied whichheats the print head by means of heating the thermal actuators to beabove a predetermined temperature of operation. Once the temperature hasachieved a predetermined temperature, the normal print cycle 105 hasbegun.

The utilization of the preheating step 104 results in a generalreduction in possible variation in factors such as viscosity etc.allowing for a narrower operating range of the device and, theutilization of lower thermal energies in ink ejection.

The preheating step can take a number of different forms. Where the inkejection device is of a thermal bend actuator type, it would normallyreceive a series of clock pulse as illustrated in FIG. 13 with theejection of ink requiring a clock pulses 110 of a predeterminedthickness so as to provide enough energy for ejection.

As illustrated in FIG. 14, when it is desired to provide for preheatingcapabilities, these can be provided through the utilization of a seriesof shorter pulses eg. 111 which whilst providing thermal energy to theprint head, fail to cause ejection of the ink from the ink ejectionnozzle.

FIG. 16 illustrates an example graph of the print head temperatureduring a printing operation. Assuming the print head has been idle for asubstantial period of time, the print

Head temperature, initially 115, will be the ambient temperature. Whenit is desired to print, a preheating step (104 of FIG. 12) is executedsuch that the temperature rises as shown at 116 to an operationaltemperature T2 at 117, at which point printing can begin and thetemperature left to fluctuate in accordance with usage requirements.

Alternately, as illustrated in FIG. 16, the print head temperature canbe continuously monitored such that should the temperature fall below athreshold eg. 120, a series of preheating cycles are injected into theprinting process so as to increase the temperature to 121, above apredetermined threshold.

Assuming the ink utilized has properties substantially similar to thatof water, the utilization of the preheating step can take advantage ofthe substantial fluctuations in ink viscosity with temperature. Ofcourse, other operational factors may be significant and thestabilisation to a narrower temperature range provides for advantageouseffects. As the viscosity changes with changing temperature, it would bereadily evident that the degree of preheating required above the ambienttemperature will be dependant upon the ambient temperature and theequilibrium temperature of the print head during printing operations.Hence, the degree of preheating may be varied in accordance with themeasured ambient temperature so as to provide for optimal results.

A simple operational schematic is illustrated in FIG. 17 with the printhead 130 including an on-board series of temperature sensors which areconnected to a temperature determination unit 131 for determining thecurrent temperature which in turn outputs to an ink ejection drive until132 which determines whether preheating is required at any particularstage. The on-chip (print head) temperature sensors can be simple MEMStemperature sensors, the construction of which is well known to thoseskilled in the art.

Manufacturing Process

IJ46 device manufacture can be constructed from a combination ofstandard CMOS processing, and MEMS postprocessing. Ideally, no materialsshould be used in the MEMS portion of the processing which are notalready in common use for CMOS processing. In the preferred embodiment,the only MEMS materials are PECVD glass, sputtered TiN, and asacrificial material (which may be polyimide, PSG, BPSG, aluminum, orother materials). Ideally, to fit corresponding drive circuits betweenthe nozzles without increasing chip area, the minimum process is a 0.5micron, one poly, 3 metal CMOS process with aluminum metallization.However, any more advanced process can be used instead. Alternatively,NMOS, bipolar, BiCMOS, or other processes may be used. CMOS isrecommended only due to its prevalence in the industry, and theavailability of large amounts of CMOS fab capacity.

For a 100 mm photographic print head using the CMY process color model,the CMOS process implements a simple circuit consisting of 19,200 statesof shift register, 19,200 bits of transfer register, 19,200 enablegates, and 19,200 drive transistors, There are also some clock buffersand enable decoders. The clock speed of a photo print head is only 3.8MHz, and a 30 ppm A4 print head is only 14 MHz, so the CMOS performanceis not critical. The CMOS process is fully completed, includingpassivation and opening of bond pads before the MEMS processing begins.This allows the CMOS processing to be completed in a standard CMOS fab,with the MEMS processing being performed in a separate facility.

Reasons for Process Choices

It will be understood from those skilled in the art of manufacture ofMEMS devices that there are many possible process sequences for themanufacture of an IJ46 print head. The process sequence described hereis based on a ‘generic’ 0.5 micron (drawn) n-well CMOS process with 1poly and three metal layers. This table outlines the reasons for some ofthe choices of this ‘nominal’ process, to make it easier to determinethe effect of any alternative

Nominal Process Reason CMOS Wide availability 0.5 micron or less 0.5micron is required to fit drive electronics under the actuators 0.5micron or more Fully amortized fabs, low cost N-well Performance ofn-channel is more important than p-channel transistors 6″ wafers Minimumpractical for 4″ monilithic print heads 1 polysilicon layer 2 polylayers are not required, as there is little low current connectivity 3metal layers To supply high currents, most of metal 3 also providessacrificial structures Aluminum Low cost, standard for 0.5 micronprocesses metalization (copper may be more efficient)Mask Summary

Mask # Mask Notes Type Pattern Align to CD 1 N-well CMOS 1 Light Flat  4 μm 2 Active Includes nozzle CMOS 2 Dark N-Well   1 μm 3 Poly CMOS 3Dark Active 0.5 μm 4 N+ CMOS 4 Dark Poly   4 μm 5 P+ CMOS 4 Light Poly  4 μm 6 Contact Includes nozzle chamber CMOS 5 Light Poly 0.5 μm 7Metal 1 CMOS 6 Dark Contact 0.6 μm 8 Via 1 Includes nozzle CMOS 7 LightMetal 1 0.6 μm 9 Metal 2 Includes sacrificial al. CMOS 8 Dark Via 1 0.6μm 10 Via 2 Includes nozzle chamber CMOS 9 Light Metal 2 0.6 μm 11 Metal3 Includes sacrificial al. CMOS 10 Dark Poly   1 μm 12 Via 3 Overcoat,but 0.6 μm CD CMOS 11 Light Poly 0.6 μm 13 Heater MEMS 1 Dark Poly 0.6μm 14 Actuator MEMS 2 Dark Heater   1 μm 15 Nozzle For CMP control MEMS3 Dark Poly   2 μm 16 Chamber MEMS 4 Dark Nozzle   2 μm 17 InletBackside deep silicon etch MEMS 5 Light Poly   4 μmExample Process Sequence (Including CMOS Steps)

Although many different CMOS and other processes can be used, thisprocess description is combined with an example CMOS process to showwhere MEMS features are integrated in the CMOS masks, and show where theCMOS process may be simplified due to the low CMOS performancerequirements.

Process steps described below are part of the example ‘generic’ IP3M 0.5micron CMOS process.

-   1. As shown in FIG. 18, processing starts with a standard 6″ p-type    <100> wafers. (8″ wafers can also be used, giving a substantial    increase in primary yield).-   2. Using the n-well mask of FIG. 19, implant the n-well transistor    portions 210 of FIG. 20.-   3. Grow a thin layer of SiO₂ and deposit Si₃N₄ forming a field oxide    hard mask.-   4. Etch the nitride and oxide using the active mask of FIG. 22. The    mask is oversized to allow for the LOCOS bird's beak. The nozzle    chamber region is incorporated in this mask, as field oxide is    excluded from the nozzle chamber. The result is a series of oxide    regions 212, illustrated in FIG. 23.-   5. Implant the channel-stop using the n-well mask with a negative    resist, or using a complement of the n-well mask.-   6. Perform any required channel stop implants as required by the    CMOS process used.-   7. Grow 0.5 micron of field oxide using LOCOS.-   8. Perform any required n/p transistor threshold voltage    adjustments. Depending upon the characteristics of the CMOS process,    it may be possible to omit the threshold adjustments. This is    because the operating frequency is only 3.8 MHz, and the quality of    the p-devices is not critical. The n-transistor threshold is more    significant, as the on-resistance of the n-channel drive transistor    has a significant effect on the efficiency and power consumption    while printing.-   9. Grow the gate oxide.-   10. Deposit 0.3 microns of poly, and pattern using the poly mask    illustrated in FIG. 25 so as to form poly portions 214 shown in FIG.    26.-   11. Perform the n+ implant shown e.g. 216 in FIG. 29 using the n+    mask shown in FIG. 28. The use of a drain engineering processes such    as LDD should not be required, as the performance of the transistors    is not critical.-   12. Perform the p+ implant shown e.g. 218 in FIG. 32, using a    complement of the n+ mask shown in FIG. 31, or using the n+ mask    with a negative resist. The nozzle chamber region will be doped    either n+ or p+ depending upon whether it is included in the n+ mask    or not. The doping of this silicon region is not relevant as it is    subsequently etched, and the STS ASE etch process recommended does    not use boron as an etch stop.-   13. Deposit 0.6 microns of PECVD TEOS glass to form ILD 1, shown    e.g. 220 in FIG. 35.-   14. Etch the contact cuts using the contact mask of FIG. 34. The    nozzle region is treated as a single large contact region, and will    not pass typical design rule checks. This region should therefore be    excluded from the DRC.-   15. Deposit 0.6 microns of aluminum to form metal 1.-   16. Etch the aluminum using the metal 1 mask shown in FIG. 37 so as    to form metal regions e.g. 224 shown in FIG. 38. The nozzle metal    region is covered with metal 1 e.g. 225. This aluminum 225 is    sacrificial, and is etched as part of the MEMS sequence. The    inclusion of metal 1 in the nozzle is not essential, but helps    reduce the step in the neck region of the actuator lever arm.-   17. Deposit 0.7 microns of PECVD TEOS glass to form ILD 2 regions    e.g. 228 of FIG. 41.-   18. Etch the contact cuts using the via 1 mask shown in FIG. 40. The    nozzle region is treated as a single large via region, and again it    will not pass DRC.-   19. Deposit 0.6 microns of aluminum to form metal 2.-   20. Etch the aluminum using the metal 2 mask shown in FIG. 42 so as    to form metal portions e.g. 230 shown in FIG. 43. The nozzle region    231 is fully covered with metal 2. This aluminum is sacrificial, and    is etched as part of the MEMS sequence. The inclusion of metal 2 in    the nozzle is not essential, but helps reduce the step in the neck    region of the actuator level arm. Sacrificial metal 2 is also used    for another fluid control feature. A relatively large rectangle of    metal 2 is included in the neck region 233 of the nozzle chamber.    This is connected to the sacrificial metal 3, so is also removed    during the MEMS sacrificial aluminum etch. The undercuts the lower    rim of the nozzle chamber entrance for the actuator (which is formed    from ILD 3). The undercut adds 90 degrees to angle of the fluid    control surface, and thus increases the ability of this rim to    prevent ink surface spread.-   21. Deposit 0.7 microns of PECVD TEOS glass to form ILD 3.-   22. Etch the contact cuts using the via 2 mask shown in FIG. 45 so    as to leave portions e.g. 236 shown in FIG. 46. As well as the    nozzle chamber, fluid control rims are also formed in ILD 3. These    will also not pass DRC.-   23. Deposit 1.0 microns of aluminum to form metal 3.-   24. Etch the aluminum using the metal 3 mask shown in FIG. 47 so as    to leave portions e.g. 238 as shown in FIG. 48. Most of metal 3 e.g.    239 is a sacrificial layer used to separate the actuator and paddle    from the chip surface. Metal 3 is also used to distribute V+ over    the chip. The nozzle region is fully covered with metal 3 e.g. 240.    This aluminum is sacrificial, and is etched as part of the MEMS    sequence. The inclusion of metal 3 in the nozzle is not essential,    but helps reduce the step in the neck region of the actuator lever    arm.-   25. Deposit 0.5 microns of PECVD TEOS glass to form the overglass.-   26. Deposit 0.5 microns of Si₃N₄ to form the passivation layer.-   27. Etch the passivation and overglass using the via 3 mask shown in    FIG. 50 so as to form the arrangement of FIG. 51. This mask includes    access 242 the metal 3 sacrificial layer, and the vias e.g. 243 to    the heater actuator. Lithography of this step has 0.6 micron    critical dimensions (for the heater vias) instead of the normally    relaxed lithography used for opening bond pads. This is the one    process step which is different from the normal CMOS process flow.    This step may either be the last process step of the CMOS process,    or the first step of the MEMS process, depending upon the fab setup    and transport requirements.-   28. Wafer Probe. Much, but not all, of the functionality of the    chips can be determined at this stage. If more complete testing at    this stage is required, an active dummy load can be included on chip    for each drive transistor. This can be achieved with minor chip area    penalty, and allows complete testing of the CMOS circuitry.-   29. Transfer the wafers from the CMOS facility to the MEMS facility.    These may be in the same fab, or may be distantly located.-   30. Deposit 0.9 microns of magnetron sputtered TiN. Voltage is −65V,    magnetron current is 7.5 A, argon gas pressure is 0.3 Pa,    temperature is 300° C. This results in a coefficient of thermal    expansion of 9.4×10⁻⁶/° C., and a Young's modulus of 600 GPa [Thin    Solid Films 270 p. 266, 1995], which are the key thin film    properties used.-   31. Etch the TiN using the heater mask shown in FIG. 53. This mask    defines the heater element, paddle arm, and paddle. There is a small    gap 247 shown in FIG. 54 between the heater and the TiN layer of the    paddle and paddle arm. This is to prevent electrical connection    between the heater and the ink, and possible electrolysis problems.    Sub-micron accuracy is required in this step to maintain a    uniformity of heater characteristics across the wafer. This is the    main reason that the heater is not etched simultaneously with the    other actuator layers. CD for the heater mask is 0.5 microns.    Overlay accuracy is +/−0.1 microns. The bond pads are also covered    with this layer of TiN. This is to prevent the bond pads being    etched away during the sacrificial aluminum etch. It also prevents    corrosion of the aluminum bond pads during operation. TiN is an    excellent corrosion barrier for aluminum. The resistivity of TiN is    low enough to not cause problems with the bond pad resistance.-   32. Deposit 2 microns of PECVD glass. This is preferably done at    around 350° C. to 400° C. to minimize intrinsic stress in the glass.    Thermal stress could be reduced by a lower deposition temperature,    however thermal stress is actually beneficial, as the glass is    sandwiched between two layers of TiN. The TiN/glass/TiN tri-layer    cancels bend due to thermal stress, and results in the glass being    under constant compressive stress, which increases the efficiency of    the actuator.-   33. Deposit 0.9 microns of magnetron sputtered TiN. This layer is    deposited to cancel bend from the differential thermal stress of the    lower TiN and glass layers, and prevent the paddle from curling when    released from the sacrificial materials. The deposition    characteristics should be identical to the first TiN layer.-   34. Anisotropically plasma etch the TiN and glass using actuator    mask as shown in FIG. 56. This mask defines the actuator and paddle.    CD for the actuator mask is 1 micron. Overlay accuracy is +/−0.1    microns. The results of the etching process is illustrated in FIG.    57 with the glass layer 250 sandwiched between TiN layers 251,248.-   35. Electrical testing can be performed by wafer probing at this    time. All CMOS tests and heater functionality and resistance tests    can be completed at wafer probe.-   36. Deposit 15 microns of sacrificial material. There are many    possible choices for this material. The essential requirements are    the ability to deposit a 15 micron layer without excessive wafer    warping, and a high etch selectivity to PECVD glass and TiN. Several    possibilities are phosphosilicate glass (PSG), borophosphosilicate    glass (BPSG), polymers such as polyimide, and aluminum. Either a    close CTE match to silicon (BPSG with the correct doping, filled    polyimide) or a low Young's modulus (aluminum) is required. This    example uses BPSG. Of these issues, stress is the most demanding due    to the extreme layer thickness. BPSG normally has a CTE well below    that of silicon, resulting in considerable compressive stress.    However, the composition of BPSG can be varied significantly to    adjust its CTE close to that of silicon. As the BPSG is a    sacrificial layer, its electrical properties are not relevant, and    compositions not normally suitable as a CMOS dielectric can be used.    Low density, high porosity, and a high water content are all    beneficial characteristics as they will increase the etch    selectivity versus PECVD glass when using an anhydrous HF etch.-   37. Etch the sacrificial layer to a depth of 2 microns using the    nozzle mask as defined in FIG. 59 so as to form the structure 254    illustrated in section in FIG. 60. The mask of FIG. 59 defines all    of the regions where a subsequently deposited overcoat is to be    polished off using CMP. This includes the nozzles themselves, and    various other fluid control features. CD for the nozzle mask is 2    microns. Overlay accuracy is +/−0.5 microns.-   38. Anisotropically plasma etch the sacrificial layer down to the    CMOS passivation layer using the chamber mask as illustrated in    FIG. 62. This mask defines the nozzle chamber and actuator shroud    including slots 255 as shown in FIG. 63. CD for the chamber mask is    2 microns, Overlay accuracy is +/−0.2 microns.-   39. Deposit 0.5 microns of fairly conformal overcoat material 257 as    illustrated in FIG. 65. The electrical properties of this material    are irrelevant, and it can be a conductor, insulator, or    semiconductor. The material should be: chemically inert, strong,    highly selective etch with respect to the sacrificial material, be    suitable for CMP, and be suitable for conformal deposition at    temperatures below 500° C. Suitable materials include: PECVD glass,    MOCVD TiN, ECR CVD TiN, PECVD Si₃N₄, and many others. The choice for    this example is PECVD TEOS glass. This must have a very low water    content if BPSG is used as the sacrificial material and anhydrous HF    is used as the sacrificial etchant, as the anhydrous HF etch relies    on water content to achieve 1000:1 etch selectivity of BPSG over    TEOS glass. The confirmed overcoat 257 forms a protective covering    shell around the operational portions of the thermal bend actuator    while permitting movement of the actuator within the shell.-   40. Planarize the wafer to a depth of 1 micron using CMP as    illustrated in FIG. 67. The CMP processing should be maintained to    an accuracy of +/−0.5 microns over the wafer surface. Dishing of the    sacrificial material is not relevant. This opens the nozzles 259 and    fluid control regions e.g. 260. The rigidity of the sacrificial    layer relative to the nozzle chamber structures during CMP is one of    the key factors which may affect the choice of sacrificial    materials.-   41. Turn the print head wafer over and securely mount the front    surface on an oxidized silicon wafer blank 262 illustrated in FIG.    69 having an oxidized surface 263. The mounting can be by way of    glue 265.

The blank wafers 262 can be recycled.

-   42. Thin the print head wafer to 300 microns using backgrinding (or    etch) and polish. The wafer thinning is performed to reduce the    subsequent processing duration for deep silicon etching from around    5 hours to around 2.5 hours. The accuracy of the deep silicon etch    is also improved, and the hard-mask thickness is halved to 2.6    microns. The wafers could be thinned further to improve etch    duration and print head efficiency. The limitation to wafer    thickness is the print head fragility after sacrificial BPSG etch.-   43. Deposit a SiO₂ hard mask (2.5 microns of PECVD glass) on the    backside of the wafer and pattern using the inlet mask as shown in    FIG. 67. The hard mask of FIG. 67 is used for the subsequent deep    silicon etch, which is to a depth of 315 microns with a hard mask    selectivity of 150:1. This mask defines the ink inlets, which are    etched through the wafer. CD for the inlet mask is 4 microns.    Overlay accuracy is +/−2 microns. The inlet mask is undersize by    5.25 microns on each side to allow for a re-entrant etch angle of 91    degrees over a 300 micron etch depth. Lithography for this step uses    a mask aligner instead of a stepper. Alignment is to patterns on the    front of the wafer. Equipment is readily available to allow    sub-micron front-to-back alignment.-   44. Back-etch completely through the silicon wafer (using, for    example, an ASE Advanced Silicon Etcher from Surface Technology    Systems) through the previously deposited hard mask. The STS ASE is    capable of etching highly accurate holes through the wafer with    aspect ratios of 30:1 and sidewalls of 90 degrees. In this case, a    re-entrant sidewall angle of 91 degrees is taken as nominal. A    re-entrant angle is chosen because the ASE performs better, with a    higher etch rate for a given accuracy, with a slightly re-entrant    angle. Also, a re-entrant etch can be compensated by making the    holes on the mask undersize. Non-re-entrant etch angles cannot be so    easily compensated, because the mask holes would merge. The wafer is    also preferably diced by this etch. The final result is as    illustrated in FIG. 69 including back etched ink channel portions    264.-   45. Etch all exposed aluminum. Aluminum on all three layers is used    as sacrificial layers in certain places.-   46. Etch all of the sacrificial material. The nozzle chambers are    cleared by this etch with the result being as shown in FIG. 71. If    BPSG is used as the sacrificial material, it can be removed without    etching the CMOS glass layers or the actuator glass. This can be    achieved with 1000:1 selectivity against undoped glass such as TEOS,    using anhydrous HF at 1500 sccm in a N₂ atmosphere at 60° C. [L.    Chang et al, “Anhydrous HF etch reduces processing steps for DRAM    capacitors”, Solid State Technology Vol. 41 No. 5, pp 71-76, 1998].    The actuators are freed and the chips are separated from each other,    and from the blank wafer, by this etch. If aluminum is used as the    sacrificial layer instead of BPSG, then its removal is combined with    the previous step, and this step is omitted.-   47. Pick up the loose print heads with a vacuum probe, and mount the    print heads in their packaging. This must be done carefully, as the    unpackaged print heads are fragile. The front surface of the wafer    is especially fragile, and should not be touched. This process    should be performed manually, as it is difficult to automate. The    package is a custom injection molded plastic housing incorporating    ink channels that supply the appropriate color ink to the ink inlets    at the back of the print head. The package also provides mechanical    support to the print head. The package is especially designed to    place minimal stress on the chip, and to distribute that stress    evenly along the length of the package. The print head is glued into    this package with a compliant sealant such as silicone.-   48. Form the external connections to the print head chip. For a low    profile connection with minimum disruption of airflow, tape    automated bonding (TAB) may be used. Wire bonding may also be used    if the printer is to be operated with sufficient clearance to the    paper. All of the bond pads are along one 100 mm edge of the chip.    There are a total of 504 bond pads, in 8 identical groups of 63 (as    the chip is fabricated using 8 stitched stepper steps). Each bond    pad is 100×100 micron, with a pitch of 200 micron. 256 of the bond    pads are used to provide power and ground connections to the    actuators, as the peak current is 6.58 Amps at 3V. There are a total    of 40 signal connections to the entire print head (24 data and 16    control), which are mostly bussed to the eight identical sections of    the print head.-   49. Hydrophobize the front surface of the print heads. This can be    achieved by the vacuum deposition of 50 nm or more of    polytetrafluoroethylene (PTFE). However, there are also many other    ways to achieve this. As the fluid is fully controlled by mechanical    protuberances formed in previous steps, the hydrophobic layer is an    ‘optional extra’ to prevent ink spreading on the surface if the    print head becomes contaminated by dust.-   50. Plus the print heads into their sockets. The socket provides    power, data, and ink. The ink fills the print-head by capillarity.    Allow the completed print heads to fill with ink, and test. FIG. 74    illustrates the filling of ink 268 into the nozzle chamber.    Process Parameters Used for this Implementation Example

The CMOS process parameters utilized can be varied to suit any CMOSprocess of 0.5 micron dimensions or better. The MEMS process parametersshould not be varied beyond the tolerances shown below. Some of theseparameters affect the actuator performance and fluidics, while othershave more obscure relationships. For example, the wafer thin stageaffects the cost and accuracy of the deep silicon etch, the thickness ofthe back-side hard mask, and the dimensions of the associated plasticink channel molding. Suggested process parameters can be as follows:

Parameter Type Min. Nom. Max Units Tol. Wafer resistivity CMOS 15 20 25Ω cm ±25% Wafer thickness CMOS 600 650 700 μm  ±8% N-Well Junction depthCMOS 2 2.5 3 μm ±20% n+ Junction depth CMOS 0.15 0.2 0.25 μm ±25% p+Junction depth CMOS 0.15 0.2 0.25 μm ±25% Field oxide thickness CMOS0.45 0.5 0.55 μm ±10% Gate oxide thickness CMOS 12 13 14 Nm  ±7% Polythickness CMOS 0.27 0.3 0.33 μm ±10% ILD 1 thickness (PECVC glass) CMOS0.5 0.6 0.7 μm ±16% Metal 1 thickness (aluminum) CMOS 0.55 0.6 0.65 μm ±8% ILD 2 thickness (PECVD glass) CMOS 0.6 0.7 0.8 μm ±14% Metal 2thickness (aluminum) CMOS 0.55 0.6 0.65 μm  ±8% ILD 3 thickness (PECVDglass) CMOS 0.6 0.7 0.8 μm ±14% Metal 3 thickness (aluminum) CMOS 0.91.0 1.1 μm ±10% Overcoat (PECVD glass) CMOS 0.4 0.5 0.6 μm ±20%Passivation (Si₃N₄) CMOS 0.4 0.5 0.6 μm ±20% Heater thickness (TiN) MEMS0.85 0.9 0.95 μm  ±5% Actuator thickness (PECVD glass) MEMS 1.9 2.0 2.1μm  ±5% Bend compensator thickness (TiN) MEMS 0.85 0.9 0.95 μm  ±5%Sacriificial layer thickness (low stress BPSG) MEMS 13.5 15 16.5 μm ±10%Nozzle etch (BPSG) MEMS 1.6 2.0 2.4 μm ±20% Nozzle chamber and shroudMEMS 0.3 0.5 0.7 μm ±40% (PECVC glass) Nozzle CMP depth MEMS 0.7 1 1.3μm ±30% Wafer thin (back-grind and polish) MEMS 295 300 305 μm ±1.6% Back-etch hard mask (SiO₂) MEMS 2.25 2.5 2.75 μm ±10% STS ASE back-etch(stop on MEMS 305 325 345 μm  ±6% aluminum)Control Logic

Turning over to FIG. 76, there is illustrated the associated controllogic for a single ink jet nozzle. The control logic 280 is utilized toactivate a heater element 281 on demand. The control logic 280 includesa shift register 282, a transfer register 283 and a firing control gate284. The basic operation is to shift data from one shift register 282 tothe next until it is in place. Subsequently, the data is transferred toa transfer register 283 upon activation of a transfer enable signal 286.The data is latched in the transfer register 283 and subsequently, afiring phase control signal 289 is utilized to activate a gate 284 foroutput of a heating pulse to heat an element 281.

As the preferred implementation utilizes a CMOS layer for implementationof all control circuitry, one form of suitable CMOS implementation ofthe control circuitry will now be described. Turning now to FIG. 77,there is illustrated a schematic block diagram of the corresponding CMOScircuitry. Firstly, shift register 282 takes an inverted data input andlatches the input under control of shift clocking signals 291, 292. Thedata input 290 is output 294 to the next shift register and is alsolatched by a transfer register 283 under control of transfer enablesignals 296, 297. The enable gate 284 is activated under the control ofenable signal 299 so as to drive a power transistor 300 which allows forresistive heating of resistor 281. The functionality of the shiftregister 282, transfer register 283 and enable gate 284 are standardCMOS components well understood by those skilled in the art of CMOScircuit design.

Replicated Units

The ink jet print head can consist of a large number of replicated unitcells each of which has basically the same design. This design will nowbe discussed.

Turning initially to FIG. 78, there is illustrated a general key orlegend of different material layers utilized in subsequent discussions.

FIG. 79 illustrates the unit cell 305 on a 1 micron grid 306. The unitcell 305 is copied and replicated a large number of times with FIG. 79illustrating the diffusion and poly-layers in addition to vias e.g. 308.The signals 290, 291, 292, 296, 297 and 299 are previously discussedwith reference to FIG. 77. A number of important aspects of FIG. 79include the general layout including the shift register, transferregister and gate and drive transistor. Importantly, the drivetransistor 300 includes an upper poly-layer e.g. 309 which is laid outhaving a large number of perpendicular traces e.g. 312. Theperpendicular traces are important in ensuring that the corrugatednature of a heater element formed over the power transistor 300 willhave a corrugated bottom with corrugations running generally in theperpendicular direction of trace 112. This is best shown in FIGS. 69, 71and 74. Consideration of the nature and directions of the corrugations,which arise unavoidably due to the CMOS wiring underneath, is importantto the ultimate operational efficiency of the actuator. In the idealsituation, the actuator is formed without corrugations by including aplanarization step on the upper surface of the substrate step prior toforming the actuator. However, the best compromise that obviates theadditional process step is to ensure that the corrugations extend in adirection that is transverse to the bending axis of the actuator asillustrated in the examples, and preferably constant along its length.This results in an actuator that may only be 2% less efficient than aflat actuator, which in many situations will be an acceptable result. Bycontrast, corrugations that extend longitudinally would reduce theefficiency by about 20% compared to a flat actuator.

In FIG. 80, there is illustrated the addition of the first level metallayer which includes enable lines 296, 297.

In FIG. 81, there is illustrated the second level metal layer whichincludes data in-line 290, SClock line 91, SClock 292, Q 294, TEn 296and TEn 297, V-320, V_(DD) 321, V_(SS) 322, in addition to associatedreflected components 323 to 328. The portions 330 and 331 are utilizedas a sacrificial etch.

Turning now to FIG. 82 there is illustrated the third level metal layerwhich includes a portion 340 which is utilized as a sacrificial etchlayer underneath the heater actuator. The portion 341 is utilized aspart of the actuator structure with the portions 342 and 343 providingelectrical interconnections.

Turning now to FIG. 83, there is illustrated the planar conductiveheating circuit layer including heater arms 350 and 351 which areinterconnected to the lower layers. The heater arms are formed on eitherside of a tapered slot so that they are narrower toward the fixed orproximal end of the actuator arm, giving increased resistance andtherefore heating and expansion in that region. The second portion ofthe heating circuit layer 352 is electrically isolated from the arms 350and 351 by a discontinuity 355 and provides for structural support forthe main paddle 356. The discontinuity may take any suitable form but istypically a narrow slot as shown at 355.

In FIG. 84 there is illustrated the portions of the shroud and nozzlelayer including shroud 353 and outer nozzle chamber 354.

Turning to FIG. 85, there is illustrated a portion 360 of a array of inkejection nozzles which are divided into three groups 361-363 with eachgroup providing separate color output, (cyan, magenta and yellow) so asto provide full three color printing. A series of standard cell clockbuffers and address decoders 364 is also provided in addition to bondpads 365 for interconnection with the external circuity.

Each color group 361, 363 consists of two spaced apart rows of inkejection nozzles e.g. 367 each having a heater actuator element.

FIG. 87 illustrates one form of overall layout in a cut away manner witha first area 370 illustrating the layers up to the polysilicon level. Asecond area 371 illustrating the layers up to the first level metal, theare 372 illustrating the layers up to the second level metal and thearea 373 illustrating the layers up to the heater actuator layer.

The ink ejection nozzles are grouped in two groups of 10 nozzles sharinga common ink channel through the wafer. Turning to FIG. 88, there isillustrated the back surface of the wafer which includes a series of inksupply channels 380 for supplying ink to a front surface.

Replication

The unit cell is replicated 19,200 times on the 4″ print head, in thehierarchy as shown in the replication hierarchy table below. The layoutgrid is 1/21 at 0.5 micron (0.125 micron). Many of the ideal transformdistances fall exactly on a grid point. Where they do not, the distanceis rounded to the nearest grid point. The rounded numbers are shown withan asterisk. The transforms are measured from the center of thecorresponding nozzles in all cases. The transform of a group of fiveeven nozzles into five odd nozzles also involves a 180° rotation. Thetranslation for this step occurs from a position where all five pairs ofnozzle centers are coincident.

Replication Hierarchy Table

Y X Transform Replication Replication Total Transform Grid Actual GridActual Replication Stage Rotation (°) Ratio Nozzles pixels Units MicronsPixels units microns 0 Initial rotation 45 1:1 1  0    0 0 0  0 0 1 Evennozzles 0 5:1 5  2   254 31.75   1/10  13* 1.625* in a pod 2 Odd nozzles180 2:1 10  1   127 15.875 1 19/16  198* 24.75* In a pod 3 Pods in a 03:1 30 5½   699* 87.375* 7 889 111.125 CMY tripod 4 Tripods per 0 10:1 300  10  1270 158.75 0  0 0 pdgroup 5 Podgroups per 0 2:1 600 100  127001587.5 0  0 0 firegroup 6 Firegroups per 0 4:1 2400 200  25400 3175 0  00 segment 7 Segments per 0 8:1 19200 800 101600 12700 0  0 0 print headComposition

Taking the example of a 4-inch print head suitable for use in cameraphotoprinting as illustrated in FIG. 89, a 4-inch print head 380consists of 8 segments eg. 381, each segment is ½ an inch in length.Consequently each of the segments prints bi-level cyan, magenta andyellow dots over a different part of the page to produce the finalimage. The positions of the 8 segments are shown in FIG. 89. In thisexample, the print head is assumed to print dots at 1600 dpi, each dotis 15.875 microns in diameter. Thus each half-inch segment prints 800dots, with the 8 segments corresponding to positions as illustrated inthe following table:

Segment First Dot Last Dot 0 0 799 1 800 1599 2 1600 2399 3 2400 3199 43200 3999 5 4000 4799 6 4800 5599 7 5600 6399

Although each segment produces 800 dots of the final image, each dot isrepresented by a combination of bi-level cyan, magenta, and yellow ink.Because the printing is bi-level, the input image should be dithered orerror-diffused results.

Each segment 381 contains 2,400 nozzles: 800 each of cyan, magenta, andyellow. A four-inch printhead contains 8 such segments for a total of19,200 nozzles.

The nozzles within a single segment are grouped for reasons of physicalstability as well as minimization of power consumption during printing.In terms of physical stability, as shown in FIG. 88 groups of 10 nozzlesare grouped together and share the same ink channel reservoir. In termsof power consumption, the groupings are made so that only 96 nozzles arefired simultaneously from the entire print head. Since the 96 nozzlesshould be maximally distant, 12 nozzles are fired from each segment. Tofire all 19,200 nozzles, 200 different sets of 96 nozzles must be fired.

FIG. 90 shows schematically, a single pod 395 which consists of 10nozzles numbered 1 to 10 sharing a common ink channel supply. 5 nozzlesare in one row, and 5 are in another. Each nozzle produces dots 15.875μm in diameter. The nozzles are numbered according to the order in whichthey must be fired.

Although the nozzles are fired in this order, the relationship ofnozzles and physical placement of dots on the printed page is different.The nozzles from one row represent the even dots from one line on thepage, and the nozzles on the other row represent the odd dots from theadjacent line on the page. FIG. 91 shows the same pod 395 with thenozzles numbered according to the order in which they must be loaded.

The nozzles within a pod are therefore logically separated by the widthof 1 dot. The exact distance between the nozzles will depend on theproperties of the ink jet firing mechanism. In the best case, the printhead could be designed with staggered nozzles designed to match the flowof paper. In the worst case there is an error of 1/3200 dpi. While thiserror would be viewable under a microscope for perfectly straight lines,it certainly will not be an apparent in a photographic image.

As shown in FIG. 92, three pods representing Cyan 398, Magenta 197, andYellow 396 units, are grouped into a tripod 400. A tripod represents thesame horizontal set of 10 dots, but on different lines. The exactdistance between different color pods depends on the ink jet operatingparameters, and may vary from one ink jet to another. The distance canbe considered to be a constant number of dot-widths, and must thereforebe taken into account when printing: the dots printed by the cyannozzles will be for different lines than those printed by the magenta oryellow nozzles. The printing algorithm must allow for a variabledistance up to about 8 dot-widths.

As illustrated in FIG. 93, 10 tripods eg. 404 are organized into asingle podgroup 405. Since each tripod contains 30 nozzles, eachpodgroup contains 300 nozzles: 100 cyan, 100 magenta and 100 yellownozzles. The arrangement is shown schematically in FIG. 93, with tripodsnumbered 0-9. The distance between adjacent tripods is exaggerated forclarity.

As shown in FIG. 94, two podgroups (PodgroupA 410 and PodgroupB 411) areorganized into a single firegroup 414, with 4 firegroups in each segment415. Each segment 415 contains 4 firegroups. The distance betweenadjacent firegroups is exaggerated for clarity.

Name Replication Nozzle of Grouping Composition Ratio Count Nozzle Baseunit 1:1 1 Pod Nozzles per pod 10:1  10 Tripod Pods per CMY tripod 3:130 Podgroup Tripods per podgroup 10:1  300 Firegroup Podgroups perfiregroup 2:1 600 Segment Firegroups per segment 4:1 2,400 Print headSegments per print head 8:1 19,200Load and Print Cycles

The print head contains a total of 19,200 nozzles. A Print Cycleinvolves the firing of up to all of these nozzles, dependent on theinformation to be printed. A Load Cycle involves the loading up of theprint head with the information to be printed during the subsequentPrint Cycle.

Each nozzle has an associated NozzleEnable (289 of FIG. 76) bit thatdetermines whether or not the nozzle will fire during the Print Cycle.The NozzleEnable bits (one per nozzle) are loaded via a set of shiftregisters.

Logically there are 3 shift registers per color, each 800 deep. As bitsare shifted into the shift register they are directed to the lower andupper nozzles on alternate pulses. Internally, each 800-deep shiftregister is comprised of two 400-deep shift registers: one for the uppernozzles, and one for the lower nozzles. Alternate bits are shifted intothe alternate internal registers. As far as the external interface isconcerned however, there is a single 800 deep shift register.

Once all the shift registers have been fully loaded (800 pulses), all ofthe bits are transferred in parallel to the appropriate NozzleEnablebits. This equates to a single parallel transfer of 19,200 bits. Oncethe transfer has taken place, the Print Cycle can begin. The Print Cycleand the Load Cycle can occur simultaneously as long as the parallel loadof all NozzleEnable bits occurs at the end of the Print Cycle.

In order to print a 6″×4″ image at 1600 dpi in say 2 seconds, the 4″print head must print 9,600 lines (6×1600). Rounding up to 10,000 linesin 2 seconds yields a line time of 200 microseconds. A single PrintCycle and a single Load Cycle must both finish within this time. Inaddition, a physical process external to the print head must move thepaper an appropriate amount.

Load Cycle

The Load Cycle is concerned with loading the print head's shiftregisters with the next Print Cycle's NozzleEnable bits.

Each segment has 3 inputs directly related to the cyan, magenta, andyellow pairs of shift registers. These inputs are called CDataIn,MDataIn, and YDataIn. Since there are 8 segments, there are a total of24 color input lines per print head. A single pulse on the SRClock line(shared between all 8 segments) transfers 24 bits into the appropriateshift registers. Alternate pulses transfer bits to the lower and uppernozzles respectively. Since there are 19,200 nozzles, a total of 800pulses are required for the transfer. Once all 19,200 bits have beentransferred, a single pulse on the shared PTransfer line causes theparallel transfer of data from the shift registers to the appropriateNozzleEnable bits. The parallel transfer via a pulse on PTransfer musttake place after the Print Cycle has finished. Otherwise theNozzleEnable bits for the line being printed will be incorrect.

Since all 8 segments are loaded with a single SRClock pulse, theprinting software must produce the data in the correct sequence for theprint head. As an example, the first SRClock pulse will transfer the C,M, and Y bits for the next Print Cycle's dot 0, 800, 1600, 2400, 3200,4000, 4800, and 5600. The second SRClock pulse will transfer the C, M,and Y bits for the next Print Cycle's dot 1, 801, 1601, 2401, 3201,4001, 4801 and 5601. After 800 SRClock pulses, the Ptransfer pulse canbe given.

It is important to note that the odd and even C, M, and Y outputs,although printed during the same Print Cycle, do not appear on the samephysical output line. Thy physical separation of odd and even nozzleswithin the print head, as well as separation between nozzles ofdifferent colors ensures that they will produce dots on different linesof the page. This relative difference must be accounted for when loadingthe data into the print head. The actual difference in lines depends onthe characteristics of the ink jet used in the print head. Thedifferences can be defined by variables D₁ and D₂ where D₁ is thedistance between nozzles of different colors (likely value 4 to 8), andD₂ is the distance between nozzles of the same color (likely value =1).Table 3 shows the dots transferred to segment n of a print head on thefirst 4 pulses.

Yellow Magenta Cyan Pulse Line Dot Line Dot Line Dot 1 N 800S N + D₁800S N + 2D₁ 800S 2 N + D₂ 800S + 1 N + D₁ + D₂ 800S + 1 N + 2D₁ + D₂800S + 1 3 N 800S + 2 N + D₁ 800S + 2 N + 2D₁ 800S + 2 4 N + D₂ 800S + 3N + D₁ + D₂ 800S + 3 N + 2D₁ + D₂ 800S + 3

And so on for all 800 pulses. The 800 SRClock pulses (each clock pulsetransferring 24 bits) must take place within the 200 microseconds linetime. Therefore the average time to calculate the bit value for each ofthe 19, 200 nozzles must not exceed 200 microseconds/19200=10nanoseconds. Data can be clocked into the print head at a maximum rateof 10 MHz, which will load the data in 80 microseconds. Clocking thedata in at 4 MHz will load the data in 200 microseconds.

Print Cycle

The print head contains 19,200 nozzles. To fire them all at once wouldconsume too much power and be problematic in terms of ink refill andnozzle interference. A single print cycle therefore consists of 200different phases. 96 maximally distant nozzles are fired in each phase,for a total of 19,200 nozzles.

-   -   −4 bits TripodSelect (select 1 of 10 tripods from a firegroup)

The 96 nozzles fired each round equate to 12 per segment (since allsegments are wired up to accept the same print signals). The 12 nozzlesfrom a given segment come equally from each firegroup. Since there are 4firegroups, 3 nozzles fire from each firegroup. The 3 nozzles are oneper color. The nozzles are determined by:

-   -   4 bits NozzleSelect (select 1 of 10 nozzles from a pod)

The duration of the firing pulse is given by the AEnable and BEnablelines, which fire the PodgroupA and PodgroupB nozzles from allfiregroups respectively. The duration of a pulse depends on theviscosity of the ink (dependent on temperature and ink characteristics)and the amount of power available to the print head. The AEnable andBEnable are separate lines in order that the firing pulses can overlap.Thus the 200 phases of a Print Cycle consist of 100 A phases and 100 Bphases, effectively giving 100 sets of Phase A and Phase B.

When a nozzle fires, it takes approximately 100 microseconds to refill.This is not a problem since the entire Print Cycle takes 200microseconds. The firing of a nozzle also causes perturbations for alimited time within the common ink channel of that nozzle's pod. Theperturbations can interfere with the firing of another nozzle within thesame pod. Consequently, the firing of nozzles within a pod should beoffset by at least this amount. The procedure is to therefore fire threenozzles from a tripod (one nozzle per color) and then move onto the nexttripod within the podgroup. Since there are 10 tripods in a givenpodgroup, 9 subsequent tripods must fire before the original tripod mustfire its next three nozzles. The 9 firing intervals of 2 microsecondsgives an ink settling time of 18 microseconds.

Consequently, the firing order is:

-   -   TripodSelect 0, NozzleSelect 0 (Phases A and B)    -   TripodSelect 1, NozzleSelect 0 (Phases A and B)    -   TripodSelect 2, NozzleSelect 0 (Phases A and B)    -   . . .    -   TripodSelect 9, NozzleSelect 0 (Phases A and B)    -   TripodSelect 0, NozzleSelect 1 (Phases A and B)    -   TripodSelect 1, NozzleSelect 1 (Phases A and B)    -   TripodSelect 2, NozzleSelect 1 (Phases A and B)    -   . . .    -   TripodSelect 8, NozzleSelect 9, Phases A and B)    -   TripodSelect 9, NozzleSelect 9 (Phases A and B)

Note that phases A and B can overlap. The duration of a pulse will alsovary due to battery power and ink viscosity (which changes withtemperature). FIG. 95 shows the AEnable and BEnable lines during atypical Print Cycle.

Feedback from the Print Head

The print head produces several lines of feedback (accumulated from the8 segments). The feedback lines can be used to adjust the timing of thefiring pulses. Although each segment produces the same feedback, thefeedback from all segments share the same tri-state bus lines.Consequently only one segment at a time can provide feedback. A pulse onthe SenseEnable line ANDed with data on CYAN enables the sense lines forthat segment. The feedback sense lines are as follows:

-   -   Tsense informs the controller how hot the print head is. This        allows the controller to adjust timing of firing pulses, since        temperature affects the viscosity of the ink.    -   Vsense informs the controller how much voltage is available to        the actuator. This allows the controller to compensate for a        flat battery or high voltage source by adjusting the pulse        width.    -   Rsense_informs the controller of the resistivity (Ohms per        square) of the actuator heater. This allows the controller to        adjust the pulse widths to maintain a constant energy        irrespective of the heater sensitivity.

Wsense informs the controller of the width of the critical part of theheater, which may vary up to ±5% due to lithographic and etchingvariations. This allows the controller to adjust the pulse widthappropriately.

Preheat Mode

The printing process has a strong tendency to stay at the equilibriumtemperature. To ensure that the first section of the printed photographhas a consistent dot size, ideally the equilibrium temperature should bemet before printing any dots. This is accomplished via a preheat mode.

The Preheat mode involves a single Load Cycle to all nozzles with 1 s(i.e. setting all nozzles to fire), and a number of short firing pulsesto each nozzle. The duration of the pulse must be insufficient to firethe drops, but enough to heat up the ink surrounding the heaters.Altogether about 200 pulses for each nozzles are required, cyclingthrough in the same sequence as a standard Print Cycle.

Feedback during the Preheat mode is provided by Tsense, and continuesuntil an equilibrium temperature is reached (about 30° C. aboveambient). The duration of the Preheat mode can be around 50milliseconds, and can be tuned in accordance with the ink composition.

Print Head Interface Summary

The print head has the following connections:

Name #Pins Description Tripod Select 4 Select which tripod will fire(0-9) NozzleSelect 4 Select which nozzle from the pod will fire (0-9)AEnable 1 Firing pule for podgroup A BEnable 1 Firing pulse for podgroupB CDataIn[0-7] 8 Cyan input to cyan shift register of segments 0-7MDataIn[0-7] 8 Magenta input to magenta shift register of segments 0-7YDataIn[0-7] 8 Yellow input to yellow shift register of segments 0-7SRClock 1 A pulse on SRClock (ShiftRegisterClock) loads the currentvalues from CDataIn[0-7], MDataIn[0-7] and YdataIn[0- CdataIn[0-7],MDataIn[0-7] and YDataIn[0-7] into the 24 shift registers Ptransfer 1Parallel transfer of data from the shift registers to the internalNozzleEnable bits (one per nozzle) SenseEnable 1 A pulse on SenseEnableANDed with data on CDataIn[n] enables the sense lines for segment n.Tsense 1 Temperature sense Vsense 1 Voltage sense Rsense 1 Resistivitysense Wsense 1 Width sense Logic GND 1 Logic ground Logid PWR 1 Logicpower V− Bus bars V+ TOTAL 43 

Internal to the print head, each segment has the following connectionsto the bond pads:

PadConnections

Although an entire print head has a total of 504 connections, the masklayout contains only 63. This is because the chip is composed of eightidentical and separate sections, each 12.7 micron long. Each of thesesections has 63 pads at a pitch of 200 microns. There is an extra 50microns at each end of the group of 63 pads, resulting in an exactrepeat distance of 12,700 microns (12.7 micron, ½″)

Pads

No Name Function 1 V− Negative actuator supply 2 V_(SS) Negative drivelogic supply 3 V+ Positive actuator supply 4 V_(dd) Positive drive logicsupply 5 V− Negative actuator supply 6 SClk Serial data transfer clock 7V+ Positive actuator supply 8 TEn Parallel transfer enable 9 V− Negativeactuator supply 10 EPEn Even phase enable 11 V+ Positive actuator supply12 OPEn Odd phase enable 13 V− Negative actuator supply 14 NA[0] NozzleAddress [0] (in pod) 15 V+ Positive actuator supply 16 NA[1] NozzleAddress [1] (in pod) 17 V− Negative actuator supply 18 NA[2] NozzleAddress [2] (in pod) 19 V+ Positive actuator supply 20 NA[3] NozzleAddress [3] (in pod) 21 V− Negative actuator supply 22 PA[0] Pod Address[0] (1 of 10) 23 V+ Positive actuator supply 24 PA[1] Pod Address [1] (1of 10) 25 V− Negative actuator supply 26 PA[2] Pod Address [2] (1 of 10)27 V+ Positive actuator supply 28 PA[3] Pod Address [3] (1 of 10) 29 V−Negative actuator supply 30 PGA[0] Podgroup Address [0] 31 V+ Positiveactuator supply 32 FGA[0] Firegroup Address [0] 33 V− Negative actuatorsupply 34 FGA[1] Firegroup Address [1] 35 V+ Positive actuator supply 36SEn Sense Enable 37 V− Negative actuator supply 38 Tsense Temperaturesense 39 V+ Positive actuator supply 40 Rsense Actuator resistivitysense 41 V− Negative actuator supply 42 Wsense Actuator width sense 43V+ Positive actuator supply 44 Vsense Power supply voltage sense 45 V−Negative actuator supply 46 N/C Spare 47 V+ Positive actuator supply 48D[C] Cyan serial data in 49 V− Negative actuator supply 50 D[M] Magentaserial data in 51 V+ Positive actuator supply 52 D[Y] Yellow serial datain 53 V− Negative actuator supply 54 Q[C] Cyan data out (for testing) 55V+ Positive actuator supply 56 Q[M] Magenta data out (for testing) 57 V−Negative actuator supply 58 Q[Y] Yellow data out (for testing) 59 V+Positive actuator supply 60 V_(SS) Negative drive logic supply 61 V−Negative actuator supply 62 V_(dd) Positive drive logic supply 63 V+Positive actuator supplyFabrication and Operational Tolerances

Cause of Parameter variation Compensation Min. Nom. Max. Units AmbientTemperature Environmental Real-time −10 25 50 ° C. Nozzle RadiusLithographic Brightness adjust 5.3 5.5 5.7 micron Nozzle LengthProcessing Brightness adjust 0.5 1.0 1.5 micron Nozzle Tip ContactProcessing Brightness adjust 100 110 120 ° Angle Paddle RadiusLithographic Brightness adjust 9.8 10.0 10.2 micron Paddle-Chamber GapLithographic Brightness adjust 0.8 1.0 1.2 micron Chamber RadiusLithographic Brightness adjust 10.8 11.0 11.2 micron Inlet AreaLithographic Brightness adjust 5500 6000 6500 micron 2 Inlet LengthProcessing Brightness adjust 295 300 305 micron Inlet etch angleProcessing Brightness adjust 90.5 91 91.5 degrees (re-entrant) HeaterThickness Processing Real-time 0.95 1.0 1.05 micron Heater ResistivityMaterials Real-time 115 135 160 μΩ-cm Heater Young's Modulus MaterialsMask design 400 600 650 GPa Heater Density Materials Mask design 54005450 5500 kg/m³ Heater CTE Materials Mask design 9.2 9.4 9.6 10−⁶/° C.Heater Width Lithographic Real-time 1.15 1.25 1.35 micron Heater LengthLithographic Real-time 27.9 28.0 28.1 micron Actuator Glass ProcessingBrightness adjust 1.9 2.0 2.1 micron Thickness Glass Young's ModulusMaterials Mask design 60 75 90 GPa Glass CTE Materials Mask design 0.00.5 1.0 10−⁶/° C. Actuator Wall Angle Processing Mask design 85 90 95degrees Actuator to Substrate Gap Processing None required 0.9 1.0 1.1micron Bend Cancelling Layer Processing Brightness adjust 0.95 1.0 1.05micron Lever Arm Length Lithographic Brightness adjust 87.9 88.0 88.1micron Chamber Height Processing Brightness adjust 10 11.5 13 micronChamber Wall Angle Processing Brightness adjust 85 90 95 degrees ColorRelated Ink Viscosity Materials Mask design −20 Nom. +20 % Ink Surfacetension Materials Programmed 25 35 65 mN/m Ink Viscosity @ 25° C.Materials Programmed 0.7 2.5 15 cP Ink Dye Concentration MaterialsProgrammed 5 10 15 % Ink Temperature (relative) Operation None −10 0 +10° C. Ink Pressure Operation Programmed −10 0 +10 kPa Ink DryingMaterials Programmed +0 +2 +5 cP Actuator Voltage Operation Real-time2.75 2.8 2.85 V Drive Pulse Width Xtal Osc. None required 1.299 1.3001.301 microsec Drive Transistor Resistance Processing Real-time 3.6 4.14.6 W Fabrication Temp. (TiN) Processing Correct by 300 350 400 ° C.design Battery Voltage Operation Real-time 2.5 3.0 3.5 VVariation with Ambient Temperature

The main consequence of a change in ambient temperature is that the inkviscosity and surface tension changes. As the bend actuator respondsonly to differential temperature between the actuator layer and the bendcompensation layer, ambient temperature has negligible direct effect onthe bend actuator. The resistivity of the TiN heater changes onlyslightly with temperature. The following simulations are for an waterbased ink, in the temperature range 0° C. to 80° C.

The drop velocity and drop volume does not increase monotonically withincreasing temperature as one may expect. This is simply explained: asthe temperature increases, the viscosity falls faster than the surfacetension falls. As the viscosity falls, the movement of ink out of thenozzle is made slightly easier. However, the movement of the ink aroundthe piddle—from the high pressure zone at the paddle front to the lowpressure zone behind the paddle—changes even more. Thus more of the inkmovement is ‘short circuited’ at higher temperatures and lowerviscosities.

Ambient Ink Actu- Peak Paddle Paddle Drop Drop Temper- Viscos- Surfaceator Actuator Actuator Pulse Pulse Pulse Pulse Temper- Deflec- Veloc-Veloc- Vol- ature ity Tension Width Thickness Length Voltage CurrentWidth Energy ature tion ity ity ume ° C. cP dyne μm μm μm V mA μs nJ °C. μm m/s m/s pl 0 1.79 38.6 1.25 1.0 27 2.8 42.47 1.6 190 465 3.16 2.062.82 0.80 20 1.00 35.8 1.25 1.0 27 2.8 42.47 1.6 190 485 3.14 2.13 3.100.88 40 0.65 32.6 1.25 1.0 27 2.8 42.47 1.6 190 505 3.19 2.23 3.25 0.9360 0.47 29.2 1.25 1.0 27 2.8 42.47 1.6 190 525 3.13 2.17 3.40 0.78 800.35 25.6 1.25 1.0 27 2.8 42.47 1.6 190 545 3.24 2.31 3.31 0.88

The temperature of the IJ46 print head is regulated to optimize theconsistency of drop volume and drop velocity. The temperature is sensedon chip for each segment. The

temperature sense signal (Tsense) is connected to a common Tsenseoutput. The appropriate Tsense signal is selected by asserting the SenseEnable (Sen) and selecting the appropriate segment using the D[C₀₋₇]lines. The Tsense signal is digitized by the drive ASIC, and drive pulsewidth is altered to compensate for the ink viscosity change. Dataspecifying the viscosity/temperature relationship of the ink is storedin the Authentication chip associated with the ink.Variation with Nozzle Radius

The nozzle radius has a significant effect on the drop volume and dropvelocity. For this reason it is closely controlled by 0.5 micronlithography. The nozzle is formed by a 2 micron etch of the sacrificialmaterial, followed by deposition of the nozzle wall material and a CMPstep. The CMP planarizes the nozzle structures, removing the top of theovercoat, and exposed the sacrificial material inside. The sacrificialmaterial is subsequently removed, leaving a self-aligned nozzle andnozzle rim. The accuracy internal radius of the nozzle is primarilydetermined by the accuracy of the lithography, and the consistency ofthe sidewall angle of the 2 micron etch.

The following table shows operation at various nozzle radii. Withincreasing nozzle radius, the drop velocity steadily decreases. However,the drop volume peaks at around a 5.5 micron radius. The nominal nozzleradius is 5.5 microns, and the operating tolerance specification allowsa ±4% variation on this radius, giving a range of 5.3 to 5.7 microns.The simulations also include extremes outside of the nominal operatingrange (5.0 and 6.0 micron). The major nozzle radius variations willlikely be determined by a combination of the sacrificial nozzle etch andthe CMP step. This means that variations are likely to be non-local:differences between wafers, and differences between the center and theperimeter of a wafer. The between wafer differences are compensated bythe ‘brightness’ adjustment. Within wafer variations will beimperceptible as long as they are not sudden.

Ink Actu- Peak Drop Drop Nozzle Viscos- Surface ator Actuator PulsePulse Pulse Pulse Temper- Peak Paddle Paddle Veloc- Vol- Radius ityTension Width Length Voltage Current Width Energy ature PressureDeflection Velocity ity ume μm cP mN/m μm μm V mA μs nJ ° C. kPa μm m/sm/s pl 5.0 0.65 32.6 1.25 25 2.8 42.36 1.4 166 482 75.9 2.81 2.18 4.360.84 5.3 0.65 32.6 1.25 25 2.8 42.36 1.4 166 482 69.0 2.88 2.22 3.920.87 5.5 0.65 32.6 1.25 25 2.8 42.36 1.4 166 482 67.2 2.96 2.29 3.450.99 5.7 0.65 32.6 1.25 25 2.8 42.36 1.4 166 482 64.1 3.00 2.33 3.090.95 6.0 0.65 32.6 1.25 25 2.8 42.36 1.4 166 482 59.9 3.07 2.39 2.750.89Ink Supply System

A print head constructed in accordance with the aforementionedtechniques can be utilized in a print camera system similar to thatdisclosed in PCT patent application No. PCT/AU98/00544. A print head andink supply arrangement suitable for utilization in a print on demandcamera system will now be described. Starting initially with FIG. 96 andFIG. 97, there is illustrated portions of an ink supply arrangement inthe form of an ink supply unit 430. The supply unit can be configured toinclude three ink storage chambers 521 to supply three color inks to theback surface of a print head, which in the preferred form is a printhead chip 431. The ink is supplied to the print head by means of an inkdistribution molding or manifold 433 which includes a series of slotse.g. 434 for the flow of ink via closely toleranced ink outlets 432 tothe back of the print head 431. The outlets 432 are very small having awidth of about 100 microns and accordingly need to be made to a muchhigher degree of accuracy than the adjacent interacting components ofthe ink supply unit such as the housing 495 described hereafter.

The print head 431 is of an elongate structure and can be attached tothe print head aperture 435 in the ink distribution manifold by means ofsilicone gel or a like resilient adhesive 520.

Preferably, the print head is attached along its back surface 438 andsides 439 by applying adhesive to the internal sides of the print headaperture 435. In this manner the adhesive is applied only to theinterconnecting faces of the aperture and print head, and the risk ofblocking the accurate ink supply passages 380 formed in the back of theprint head chip 431 (see FIG. 88) is minimised. A filter 436 is alsoprovided that is designed to fit around the distribution molding 433 soas to filter the ink passing through the molding 433.

Ink distribution molding 433 and filter 436 are in turn inserted withina baffle unit 437 which is again attached by means of a silicone sealantapplied at interface 438, such that ink is able to, for example, flowthrough the holes 440 and in turn through the holes 434. The baffles 437can be a plastic injection molded unit which includes a number of spacedapart baffles or slats 441-443. The baffles are formed within each inkchannel so as to reduce acceleration of the ink in the storage chambers521 as may be induced by movement of the portable printer, which in thispreferred form would be most disruptive along the longitudinal extent ofthe print head, whilst simultaneously allowing for flows of ink to theprint head in response to active demand therefrom. The baffles areeffective in providing for portable carriage of the ink so as tominimize disruption to flow fluctuations during handling.

The baffle unit 437 is in turn encased in a housing 445. The housing 445can be ultrasonically welded to the baffle member 437 so as to seal thebaffle member 437 into three separate ink chambers 521. The bafflemember 437 further includes a series of pierceable end wall portions450-452 which can be pierced by a corresponding mating ink supplyconduit for the flow of ink into each of the three chambers. The housing445 also includes a series of holes 455 which are hydrophobically sealedby means of tape or the like so as to allow air within the threechambers of the baffle units to escape whilst ink remains within thebaffle chambers due to the hydrophobic nature of the holes eg. 455.

By manufacturing the ink distribution unit in separate interactingcomponents as just described, it is possible to use relativelyconventional molding techniques, despite the high degree of accuracyrequired at the interface with the print head. That is because thedimensional accuracy requirements are broken down in stages by usingsuccessively smaller components with only the smallest final memberbeing the ink distribution manifold or second member needing to beproduced to the narrower tolerances needed for accurate interaction withthe ink supply passages 380 formed in the chip.

The housing 445 includes a series of positioning protuberances eg.460-462. A first series of protuberances is designed to accuratelyposition interconnect means in the form of a tape automated bonded film470, in addition to first 465 and second 466 power and ground busbarswhich are interconnected to the TAB film 470 at a large number oflocations along the surface of the TAB film so as to provide for lowresistance power and ground distribution along the surface of the TABfilm 470 which is in turn interconnected to the print head chip 431.

The TAB film 470, which is shown in more detail in an opened state inFIGS. 102 and 103, is double sided having on its outer side adata/signal bus in the form of a plurality of longitudinally extendingcontrol line interconnects 550 which releasably connect with acorresponding plurality of external control lines. Also provided on theouter side are busbar contacts in the form of deposited noble metalstrips 552.

The inner side of the TAB film 470 has a plurality of transverselyextending connecting lines 553 that alternately connect the power supplyvia the busbars and the control lines 550 to bond pads on the print headvia region 554. The connection with the control lines occurring by meansof vias 556 that extend through the TAB film. One of the many advantagesof using the TAB film is providing a flexible means of connecting therigid busbar rails to the fragile print head chip 431.

The busbars 465, 466 are in turn connected to contacts 475, 476 whichare firmly clamped against the busbars 465, 466 by means of cover unit478. The cover unit 478 also can comprise an injection molded part andincludes a slot 480 for the insertion of an aluminum bar for assistingin cutting a printed page.

Turning now to FIG. 98 there is illustrated a cut away view of the printhead unit 430, associated platen unit 490, print roll and ink supplyunit 491 and drive power distribution unit 492 which interconnects eachof the units 430, 490 and 491.

The guillotine blade 495 is able to be driven by a first motor along thealuminum blade 498 so as to cut a picture 499 after printing hasoccurred. The operation of the system of FIG. 98 is very similar to thatdisclosed in PCT patent application PCT/AU98/00544. Ink is stored in thecore portion 500 of a print roll former 501 around which is rolled printmedia 502. The print media is fed under the control of electric motor494 between the platen 290 and print head unit 490 with the ink beinginterconnected via ink transmission channels 505 to the print head unit430. The print roll unit 491 can be as described in the aforementionedPCT specification. In FIG. 99, there is illustrated the assembled formof single printer unit 510.

Features and Advantages

The IJ46 print head has many features and advantages over other printingtechnologies. In some cases, these advantages stem from newcapabilities. In other cases, the advantages stem from the avoidance ofproblems inherent in prior art technologies. A discussion of some ofthese advantages follows.

High Resolution

The resolution of a IJ46 print head is 1,600 dots per inch (dpi) in boththe scan direction and transverse to the scan direction. This allowsfull photographic quality color images, and high quality text (includingKanji). Higher resolutions are possible: 2,400 dpi and 4,800 dpiversions have been investigated for special applications, but 1,600 dpiis chosen as ideal for most applications. The true resolution ofadvanced commercial piezoelectric devices is around 120 dpi and thermalink jet devices around 600 dpi.

Excellent Image Quality

High image quality requires high resolution and accurate placement ofdrops. The monolithic page width nature of IJ46 print heads allows dropplacement to sub-micron precision. High accuracy is also achieved byeliminating misdirected drops, electrostatic deflection, air turbulence,and eddies, and maintaining highly consistent drop volume and velocity.Image quality is also ensured by the provision of sufficient resolutionto avoid requiring multiple ink densities. Five color or 6 color ‘photo’ink jet systems can introduce halftoning artifacts in mid tones (such asflesh-tones) if the dye interaction and drop sizes are not absolutelyperfect. This problem is eliminated in binary three color systems suchas used in IJ46 print heads.

High Speed (30 ppm per print head)

The page width nature of the print head allows high-speed operation, asno scanning is required. The time to print a full color A4 page is lessthan 2 seconds, allowing full 30 page per minute (ppm) operation perprint head. Multiple print heads can be used in parallel to obtain 60ppm. 90 ppm, 120 ppm, etc. IJ46 print heads are low cost and compact, somultiple head designs are practical.

Low Cost

As the nozzle packing density of the IJ46 print head is very high, thechip area per print head can be low. This leads to a low manufacturingcost as many print head chips can fit on the same wafer.

All Digital Operation

The high resolution of the print head is chosen to allow fully digitaloperation using digital halftoning. This eliminates color non-linearity(a problem with continuous tone printers), and simplifies the design ofdrive ASICs.

Small Drop Volume

To achieve true 1,600 dpi resolution, a small drop size is required. AnIJ46 print head's drop size is one picoliter (1 pl). The drop size ofadvanced commercial piezoelectric and thermal ink jet devices is around3 pl to 30

Accurate Control of Drop Velocity

As the drop ejector is a precise mechanical mechanism, and does not relyon bubble nucleation, accurate drop velocity control is available. Thisallows low drop velocities (3-4 m/s) to be used in applications wheremedia and airflow can be controlled. Drop velocity can be accuratelyvaried over a considerable range by varying the energy provided to theactuator. High drop velocities (10 to 15 m/s) suitable for plan-paperoperation and relatively uncontrolled conditions can be achieved usingvariations of the nozzle chamber and actuator dimensions.

Fast Drying

A combination of very high resolution, very small drops, and high dyedensity allows full color printing with much less water ejected. A 1600dpi IJ46 print head ejects around 33% of the water of a 600 dpi thermalink jet printer. This allows fast drying and virtually eliminates papercockle.

Wide Temperature Range

IJ46 print heads are designed to cancel the effect of ambienttemperature. Only the change in ink characteristics with temperatureaffects operation and this can be electronically compensated. Operatingtemperature range is expected to be 0° C. to 50° C. for water basedinks.

No Special Manufacturing Equipment Required

The manufacturing process for IJ46 print heads leverages entirely fromthe established semiconductor manufacturing industry. Most ink jetsystems encounter major difficulty and expense in moving from thelaboratory to production, as high accuracy specialized manufacturingequipment is required.

High Production Capacity Available

A 6″ CMOS fab with 10,000 wafer starts per month can produce around 18million print heads per annum. An 8″ CMOS fab with 20,000 wafer startsper month can produce around 60 million print heads per annum. There arecurrently many such CMOS fabs in the world.

Low Factory Setup Cost

The factory set-up cost is low because existing 0.5 micron 6″ CMOS fabscan be used. These fabs could be fully amortized, and essentiallyobsolete for CMOS logic production. Therefore, volume production can use‘old’ existing facilities. Most of the MEMS post-processing can also beperformed in the CMOS fab.

Good Light-Fastness

As the ink is not heated, there are few restrictions on the types ofdyes that can be used. This allows dyes to be chosen for optimumlight-fastness. Some recently developed dyes from companies such asAvecia and Hoechst have light-fastness of 4. This is equal to thelight-fastness of many pigments, and considerably in excess ofphotographic dyes and of ink jet dyes in use until recently.

Good Water-Fastness

As with light-fastness, the lack of thermal restrictions on the dyeallows selection of dyes for characteristics such as water-fastness. Forextremely high water-fastness (as is required for washable textiles)reactive dyes can be used.

Excellent Color Gamut

The use of transparent dyes of high color purity allows a color gamutconsiderably wider than that of offset printing and silver halidephotography. Offset printing in particular has a restricted gamut due tolight scattering from the pigments used. With three-color systems (CMY)or four-color systems (CMYK) the gamut is necessarily limited to thetetrahedral volume between the color vertices. Therefore it is importantthat the cyan, magenta and yellow dies are as spectrally pure aspossible. A slightly wide ‘hexcone’ gamut that includes pure reds,greens, and blues can be achieved using a 6 color (CMYRGB) model. Such asix color print head can be made economically as it requires a chipwidth of only 1 mm.

Elimination of Color Bleed

Ink bleed between colors occurs if the different primary colors areprinted while the previous color is wet. While image blurring due to inkbleed is typically insignificant at 1600 dpi, ink bleed can ‘muddy’ themidtones of an image. Ink bleed can be eliminated by usingmicroemulsion-based ink, for which IJ46 print heads are highly suited.The use of microemulsion ink can also help prevent nozzle clogging andensure long-term ink stability.

High Nozzle Count

An IJ46 print head has 19,200 nozzles in a monolithic CMY three-colorphotographic print head. While this is large compared to other printheads, it is a small number compared to the number of devices routinelyintegrated on CMOS VLSI chips in high volume production. It is also lessthan 3% of the number of movable mirrors which Texas Instrumentsintegrates in its Digital Micromirror Device (DMD), manufactured usingsimilar CMOS and MEMS processes.

51,200 Nozzles per A4 Page width Print head

A four color (CMYK) IJ46 print head for page width A4/US letter printinguses two chips. Each 0.66 cm² chip has 25,600 nozzles for a total of51,200 nozzles.

Integration of Drive Circuits

In a print head with as many as 51,200 nozzles, it is essential tiintegrate data distribution circuits (shift registers), data timing, anddrive transistors with the nozzles. Otherwise, a minimum of 51,201external connections would be required. This is a severe problem withpiezoelectric ink jets, as drive circuits cannot be integrated onpiezoelectric substrates. Integration of many millions of connections iscommon in CMOS VLSI chips, which are fabricated in high volume at highyield. It is the number of off-chip connections that must be limited.

Monolithic Fabrication

IJ46 print heads are made as a single monolithic CMOS chip, so noprecision assembly is required. All fabrication is performed usingstandard CMOS VLSI and MEMS (Micro-Electro-Mechanical Systems) processesand materials. In thermal ink jet and some piezoelectric ink jetsystems, the assembly of nozzle plates with the print head chip is amajor cause of low yields, limited resolution, and limited size. Also,page width arrays are typically constructed from multiple smaller chips.The assembly and alignment of these chips is an expensive process.

Modular, Extendable for Wide Print Widths

Long page width print heads can be constructed by butting two or more100 mm IJ46 print heads together. The edge of the IJ46 print head chipis designed to automatically align to adjacent chips. One print headgives a photographic size printer, two gives an A4 printer, and fourgives an A3 printer. Larger numbers can be used for high speed digitalprinting, page width wide format printing, and textile printing.

Duplex Operation

Duplex printing at the full print speed is highly practical. Thesimplest method is to provide two print heads—one on each side of thepaper. The cost and complexity of providing two print heads is less thanthat of mechanical systems to turn over the sheet of paper.

Straight Paper Path

As there are no drums required, a straight paper path can be used toreduce the possibility of paper jams. This is especially relevant foroffice duplex printers, where the complex mechanisms required to turnover the pages are a major source of paper jams.

High Efficiency

Thermal ink jet print heads are only around 0.01% efficient (electricalenergy input compared to drop kinetic energy and increased surfaceenergy). IJ46 print heads are more than 20 times as efficient.

Self-Cooling Operation

The energy required to eject each drop is 160 nJ (0.16 microjoules), asmall fraction of that required for thermal ink jet printers. The lowenergy allows the print head to be completely cooled by the ejected ink,with only a 40° C. worst-case ink temperature rise. No heat sinking isrequired.

Low Pressure

The maximum pressure generated in an IJ46 print head is around 60 kPa(0.6 atmospheres). The pressures generated by bubble nucleation andcollapse in thermal ink jet and Bubblejet systems are typically inexcess of 10 Mpa (100 atmospheres), which is 160 times the maximum IJ46print head pressure. The high pressures in Bubblejet and thermal ink jetdesigns result in high mechanical stresses.

Low Power

A 30 ppm A4 IJ46 print head requires about 67 Watts when printing full 3color black. When printing 5% coverage, average power consumption isonly 3.4 Watts.

Low Voltage Operation

IJ46 print heads can operate from a single 3V supply, the same astypical drive ASICs. Thermal ink jets typically require at least 20 V,and piezoelectric ink jets often require more than 50 V. The IJ46 printhead actuator is designed for nominal operation at 2.8 volts, allowing a0.2 volt drop across the drive transistor, to achieve 3V chip operation.

Operation from 2 or 4 AA Batteries

Power consumption is low enough that a photographic IJ46 print head canoperate from AA batteries. A typical 6″×4″ photograph requires less than20 Joules to print (including drive transistor losses). Four AAbatteries are recommended if the photo is to be printed in 2 seconds. Ifthe print time is increased to 4 seconds, 2 AA batteries can be used.

Battery Voltage Compensation

IJ46 print heads can operate from an unregulated battery supply, toeliminate efficiency losses of a voltage regulator. This means thatconsistent performance must be achieved over a considerable range ofsupply voltages. The IJ46 print head senses the supply voltage, andadjusts actuator operation to achieve consistent drop volume.

Small Actuator and Nozzle Area

The area required by an IJ46 print head nozzle, actuator, and drivecircuit is 1764 μm². This is less than 1% of the area required bypiezoelectric ink jet nozzles, and around 5% of the area required byBubblejet nozzles. The actuator area directly affects the print headmanufacturing cost.

Small Total Print Head Size

An entire print head assembly (including ink supply channels) for an A4,30 ppm, 1,600 dpi, four color print head is 210 mm×12 mm×7 mm. The smallsize allows incorporation into notebook computers and miniatureprinters. A photograph printer is 106 mm×7 mm×7 mm, allowing inclusionin pocket digital cameras, palmtop PC's, mobile phone/fax, and so on.Ink supply channels take most of this volume. The print head chip itselfis only 102 mm×0.55 mm×0.3 mm.

Miniature Nozzle Capping System

A miniature nozzle capping system has been designed for IJ46 printheads. For a photograph printer this nozzle capping system is only 106mm×5 mm×4 mm, and does not require the print head to move.

High Manufacturing Yield

The projected manufacturing yield (at maturity) of the IJ46 print headsis at least 80%, as it is primarily a digital CMOS chip with an area ofonly 0.55 cm². Most modern CMOS processes achieve high yield with chipareas in excess of 1 cm². For chips less than around 1 cm², cost isroughly proportional to chip area. Cost increases rapidly between 1 cm²and 4 cm², with chips larger than this rarely being practical. There isa strong incentive to ensure that the chip area is less than 1 cm². Forthermal ink jet and Bubblejet print heads, the chip width is typicallyaround 5 mm, limiting the cost effective chip length to around 2 cm. Amajor target of IJ46 print head development has been to reduce the chipwidth as much as possible, allowing cost effective monolithic page widthprint heads.

Low Process Complexity

With digital IC manufacture, the mask complexity of the device haslittle or no effect on the manufacturing cost or difficulty. Cost isproportional to the number of process steps, and the lithographiccritical dimensions. IJ46 print heads use a standard 0.5 micron singlepoly triple metal CMOS manufacturing process, with an additional 5 MEMSmask steps. This makes the manufacturing process less complex than atypical 0.25 micron CMOS logic process with 5 level metal.

Simple Testing

IJ46 print heads include test circuitry that allows most testing to becompleted at the wafer probe state. Testing of all electricalproperties, including the resistance of the actuator, can be completedat this stage. However, actuator motion can only be tested after releasefrom the sacrificial materials, so final testing must be performed onthe packaged chips.

Low Cost Packaging

IJ46 print heads are packaged in an injection molded polycarbonatepackage. All connections are made using Tape Automated Bonding (TAB)technology (though wire bonding can be used as an option). Allconnections are along one edge of the chip.

No Alpha Particle Sensitivity

Alpha particle emission does not need to be considered in the packaging,as there are no memory elements except static registers, and a change ofstate due to alpha particle tracks is likely to cause only a singleextra dot to be printed (or not) on the paper.Relaxed Critical Dimensions

The critical dimension (CD) of the IJ46 print head CMOS drive circuitryis 0.5 microns. Advanced digital IC's such as microprocessors currentlyuse CDs of 0.25 microns, which is two device generations more advancedthan the IJ46 print head requires. Most of the MEMS post processingsteps have CDs of 1 micron or greater.

Low Stress during Manufacture

Devices cracking during manufacture are a critical problem with boththermal ink jet and piezoelectric devices. This limits the size of theprint head that it is possible to manufacture. The stresses involved inthe manufacture of IJ46 print heads are no greater than those requiredfor CMOS fabrication.

No Scan Banding

IJ46 print heads are full page width, so do not scan. This eliminatesone of the most significant image quality problems of ink jet printers.Banding due to other causes (mis-directed drops, print head alignment)is usually a significant problem in page width print heads.

These causes of banding have also been addressed.

‘Perfect’ Nozzle Alignment

All of the nozzles within a print head are aligned to sub-micronaccuracy by the 0.5 micron stepper used for the lithography of the printhead. Nozzle alignment of two 4″ print heads to make an A4 page widthprint head is achieved with the aid of mechanical alignment features onthe print head chips. This allows automated mechanical alignment (bysimply pushing two print head chips together) to within 1 micron. Iffiner alignment is required in specialized applications, 4″ print headscan be aligned optically.

No Satellite Drops

The very small drop size (1 pl) and moderate drop velocity (3 m/s)eliminates satellite drops, which are a major source of image qualityproblems. At around 4 m/s, satellite drops form, but catch up with themain drop. Above around 4.5 m/s, satellite drops form with a variety ofvelocities relative to the main drop. Of particular concern is satellitedrops which have a negative velocity relative to the print head, andtherefore are often deposited on the print head surface. These aredifficult to avoid when high drop velocities (around 10 m/s) are used.

Laminar Air Flow

The low drop velocity requires laminar airflow, with no eddies, toachieve good drop placement on the print medium. This is achieved by thedesign of the print head packaging. For ‘plain paper’ applications andfor printing on other ‘rough’ surfaces, higher drop velocities aredesirable. Drop velocities to 15 m/s can be achieved using variations ofthe design dimensions. It is possible to manufacture 3 colorphotographic print heads with a 4 m/s drop velocity, and 4 colorplain-paper print heads with a 15 m/s drop velocity, on the same wafer.This is because both can be made using the same process parameters.No Misdirected Drops

Misdirected drops are eliminated by the provision of a thin rim aroundthe nozzle, which prevents the spread of a drop across the print headsurface in regions where the hydrophobic coating is compromised.

No Thermal Crosstalk

When adjacent actuators are energized in Bubblejet or other thermal inkjet systems, the heat from one actuator spreads to others, and affectstheir firing characteristics. In IJ46 print heads, heat diffusing fromone actuator to adjacent actuators affects both the heater layer and thebend-cancelling layer equally, so has no effect on the paddle position.This virtually eliminates thermal crosstalk.

No Fluidic Crosstalk

Each simultaneously fired nozzle is at the end of a 300 micron long inkinlet etched through the (thinned) wafer. These ink inlets are connectedto large ink channels with low fluidic resistance. This configurationvirtually eliminates any effect of drop ejection from one nozzle onother nozzles.

No Structural Crosstalk

This is a common problem with piezoelectric print heads. It does notoccur in IJ46 print heads.

Permanent Print head

The IJ46 print heads can be permanently installed. This dramaticallylowers the production cost of consumables, as the consumable does notneed to include a print head.

No Kogation

Kogation (residues of burnt ink, solvent, and impurities) is asignificant problem with Bubblejet and other thermal ink jet printheads. IJ46 print heads do not have this problem, as the ink is notdirectly heated.

No Cavitation

Erosion caused by the violent collapse of bubbles is another problemthat limits the life of Bubblejet and other thermal ink jet print heads.IJ46 print heads do not have this problem because no bubbles are formed.

No Electromigration

No metals are used in IJ46 print head actuators or nozzles, which areentirely ceramic. Therefore, there is no problem with electromigrationin the actual ink jet devices. The CMOS metalization layers are designedto support the required currents without electromigration. This can bereadily achieved because the current considerations arise from heaterdrive power, not high speed CMOS switching.

Reliable Power Connections

While the energy consumption of IJ46 print heads are fifty times lessthan thermal ink jet print heads, the high print speed and low voltageresults in a fairly high electrical current consumption. Worst casecurrent for a photographic IJ46 print head printing in two seconds froma 3 Volt supply is 4.9 Amps. This is supplied via copper busbars to 256bond pads along the edge of the chip. Each bond pad carries a maximum of40 mA. On chip contacts and vias to the drive transistors carry a peakcurrent of 1.5 mA for 1.3 microseconds, and a maximum average of 12 mA.

No Corrosion

The nozzle and actuator are entirely formed of glass and titaniumnitride (TiN), a conductive ceramic commonly used as metalizationbarrier layers in CMOS devices. Both materials are highly resistant tocorrosion.

No Electrolysis

The ink is not in contact with any electrical potentials, so there is noelectrolysis.

No Fatigue

All actuator movement is within elastic limits, and the materials usedare all ceramics, so there is no fatigue.

No Friction

No moving surfaces are in contact, so there is no friction.

No Stiction

The IJ46 print head is designed to eliminate stiction, a problem commonto many MEMS devices. Stiction is a word combining “stick” with“friction” and is especially significant at the in MEMS due to therelative scaling of forces. In the IJ46 print head, the paddle issuspended over a hole in the substrate, eliminating thepaddle-to-substrate stiction which would otherwise be encountered.

No Crack Propagation

The stresses applied to the materials are less than 1% of that whichleads to crack propagation with the typical surface roughness of the TiNand glass layers. Corners are rounded to minimize stress ‘hotspots’. Theglass is also always under compressive stress, which is much moreresistant to crack propagation than tensile stress.

No Electrical Poling Required

Piezoelectric materials must be poled after they are formed into theprint head structure. This poling requires very high electrical fieldstrengths—around 20,000 V/cm. The high voltage requirement typicallylimits the size of piezoelectric print heads to around 5 cm, requiring100,000 Volts to pole. IJ46 print heads require no poling.

No Rectified Diffusion

Rectified diffusion—the formation of bubbles due to cyclic pressurevariations—is a problem that primarily afflicts piezoelectric ink jets.IJ46 print heads are designed to prevent rectified diffusion, as the inkpressure never falls below zero.

Elimination of the Saw Street

The saw street between chips on a wafer is typically 200 microns. Thiswould take 26% of the wafer area. Instead, plasma etching is used,requiring just 4% of the wafer area.

This also eliminates breakage during sawing.

Lithography Using Standard Steppers

Although IJ46 print heads are 100 mm long, standard steppers (whichtypically have an imaging field around 20 mm square) are used. This isbecause the print head is ‘stitched’ using eight identical exposures.Alignment between stitches is not critical, as there are no electricalconnections between stitch regions. One segment of each of 32 printheads is imaged with each stepper exposure, giving an ‘average’ of 4print heads per exposure.

Integration of Full Color on a Single Chip

IJ46 print heads integrate all of the colors required onto a singlechip. This cannot be done with page width ‘edge shooter’ ink jettechnologies.

Wide Variety of Inks

IJ46 print heads do not rely on the ink properties for drop ejection.Inks can be based on water, microemulsions, oils, various alcohols, MEK,hot melt waxes, or other solvents. IJ46 print heads can be ‘tuned’ forinks over a wide range of viscosity and surface tension. This is asignificant factor in allowing a wide range of applications.

Laminar Air Flow with no Eddies

The print head packaging is designed to ensure that airflow is laminar,and to eliminate eddies. This is important, as eddies or turbulencecould degrade image quality due to the small drop size.

Drop Repetition Rate

The nominal drop repetition rate of a photographic IJ46 print head is 5kHz, resulting in a print speed of 2 second per photo. The nominal droprepetition rate for an A4 print head is 10 kHz for 30+ppm A4 printing.The maximum drop repetition rate is primarily limited by the nozzlerefill rate, which is determined by surface tension when operated usingnon-pressurized ink. Drop repetition rates of 50 kHz are possible usingpositive ink pressure (around 20 kPa). However, 34 ppm is entirelyadequate for most low cost consumer applications. For very high-speedapplications, such as commercial printing, multiple print heads can beused in conjunction with fast paper handling. For low power operation(such as operation from 2 AA batteries) the drop repetition rate can bereduced to reduce power.

Low Head-to-Paper Speed

The nominal head to paper speed of a photographic IJ46 print head isonly 0.076 m/sec. For an A4 print head it is only 0.16 m/sec, which isabout a third of the typical scanning ink jet head speed. The low speedsimplifies printer design and improves drop placement accuracy. However,this head-to-paper speed is enough for 34 ppm printing, due to the pagewidth print head. Higher speeds can readily be obtained where required.

High Speed CMOS not Required

The clock speed of the print head shift registers is only 14 MHz for anA4/letter print head operating at 30 ppm. For a photograph printer, theclock speed is only 3.84 MHz. This is much lower than the speedcapability of the CMOS process used. This simplifies the CMOS design,and eliminates power dissipation problems when printing near-whiteimages.

Fully Static CMOS Design

The shift registers and transfer registers are fully static designs. Astatic design requires 35 transistors per nozzle, compared to around 13for a dynamic design. However, the static design has several advantages,including higher noise immunity, lower quiescent power consumption, andgreater processing tolerances.

Wide Power Transistor

The width to length ratio of the power transistor is 688. This allows a4 Ohm on-resistance, whereby the drive transistor consumes 6.7% of theactuator power when operating from 3V. This size transistor fits beneaththe actuator, along with the shift register and other logic. Thus anadequate drive transistor, along with the associated data distributioncircuits, consumes no chip area that is not already required by theactuator.

There are several ways to reduce the percentage of power consumed by thetransistor: increase the drive voltage so that the required current isless. Reduce the lithography to less than 0.5 micron, use BiCMOS orother high current drive technology, or increase the chip area, allowingroom for drive transistors which are not underneath the actuator.However, the 6.7% consumption of the present design is considered acost-performance optimum.

Range of Applications

The presently disclosed ink jet printing technology is suited to a widerange of printing systems. Major example applications include:

-   1. Color and monochrome office printers-   2. SOHO printers-   3. Home PC printers-   4. Network connected color and monochrome printers-   5. Departmental printers-   6. Photographic printers-   7. Printers incorporated into cameras-   8. Printers in 3G mobile phones-   9. Portable and notebook printers-   10. Wide format printers-   11. Color and monochrome copiers-   12. Color and monochrome facsimile machines-   13. Multi-function printers combining print, fax, scan, and copy    functions-   14. Digital commercial printers-   15. Short run digital printers-   16. Packaging printers-   17. Textile printers-   18. Short run digital printers-   19. Offset press supplemental printers-   20. Low cost scanning printers-   21. High speed page width printers-   22. Notebook computers with inbuilt page width printers-   23. Portable color and monochrome printers-   24. Label printers-   25. Ticket printers-   26. Point-of-sale receipt printers-   27. Large format CAD printers-   28. Photofinishing printers-   29. Video printers-   30. PhotoCD printers-   31. Wallpaper printers-   32. Laminate printers-   33. Indoor sign printers-   34. Billboard printers-   35. Videogame printers-   36. Photo ‘kiosk’ printers-   37. Business card printers-   38. Greeting card printers-   39. Book printers-   40. Newspaper printers-   41. Magazine printers-   42. Forms printers-   43. Digital photo album printers-   44. Medical printers-   45. Automotive printers-   46. Pressure sensitive label printers-   47. Color proofing printers-   48. Fault tolerant commercial printer arrays.

Prior Art Ink Jet Technologies

Similar capability print heads are unlikely to become available from theestablished ink jet manufacturers in the near future. This is becausethe two main contenders—thermal ink jet and piezoelectric ink jet—eachhave severe fundamental problems meeting the requirements of theapplication.

The most significant problem with thermal ink jet is power consumption.This is approximately 100 times that required for these applications,and stems from the energy—inefficient means of drop ejection. Thisinvolves the rapid boiling of water to produce a vapor bubble whichexpels the ink. Water has a very high heat capacity, and must besuperheated in thermal ink jet applications. The high power consumptionlimits the nozzle packing density, as

The most significant problem with piezoelectric ink jet is size andcost. Piezoelectric crystals have a very small deflection at reasonabledrive voltages, and therefore require a large area for each nozzle.Also, each piezoelectric actuator must be connected to its drive circuiton a separate substrate. This is not a significant problem at thecurrent limit of around 300 nozzles per print head, but is a majorimpediment to the fabrication of page width print heads with 19,200nozzles.

Comparison of IJ46 print heads and Thermal Ink jet (TIJ) printingmechanisms

TIJ print IJ46 print Factor heads heads Advantage Resolution 600 1,600Full photographic image quality and high quality text Printer typeScanning Page width IJ46 print heads do not scan, resulting in fasterprinting and smaller size Print speed <1 ppm 30 ppm IJ46 print head'spage width results in >30 times faster operation Number of 30051,200 >100 times as many nozzles enables the nozzles high print speedDrop volume 20 picoliters 1 picoliter Less water on the paper, print isimmediately dry, no ‘cockle’ Construction Multi-part Monolithic IJ46print heads do not require high precision assembly Efficiency <0.1% 2%20 times increase in efficiency results in low power operation Powersupply Mains power Batteries Battery operation allows portable printers,e.g. in cameras, phones Peak pressure >100 atm 0.6 atm The highpressures in a thermal ink jet cause reliability problems Inktemperature +300° C. +50° C. High ink temperatures cause burnt dyedeposits (kogation) Cavitation Problem None Cavitation (erosion due tobubble collapse) limits head life Head life Limited Permanent TIJ printheads are replaceable due to cavitation and kogation Operating 20 V 3 VAllows operation from small batteries, voltage important for portableand pocket printers Energy per drop 10 μJ 160 nJ < 1/50 of the dropejection energy allows battery operation Chip area per 40,000 μm² 1,764μm² Small size allows low cost manufacture nozzle

In the preferred embodiment, a paddle is formed with a “poker” deviceattached in a central portion thereof such that, during movement of thepaddle, the poker device pokes any unwanted foreign body or materialwhich should congregate around the nozzle, out of the nozzle. The pokercan be formed during fabrication of the ink ejection nozzle arrangementby means of a chemical mechanical planarization step with, preferably,the formation being a byproduct of the normal formation steps forforming the ink ejection nozzle on arrangement on a semi-conductor waferutilizing standard MEMS processing techniques.

Additionally, in order to restrict the amount of wicking and theopportunities for wicking, an actuator slot guard is provided, formed onthe bend actuator itself, closely adjacent to the actuator slot so as torestrict the opportunities for flow of fluid out of the nozzle chamberdue to surface tension effects.

Turning now to FIG. 1 to FIG. 3 there will now be explained theoperational principles of the preferred embodiment. In FIG. 1, there isillustrated a nozzle arrangement 201 which is formed on the substrate202 which can comprise a semi-conductor substrate or the like. Thearrangement 201 includes a nozzle chamber 203 which is normally filledwith ink so as to form a meniscus 204 which surrounds a nozzle rim 205.A thermal bend actuator device 206 is attached to post 207 and includesa conductive heater portion 209 which is normally balanced with acorresponding layer 210 in thermal equilibrium. The actuator 206 passesthrough a slot in the wall 212 of the nozzle chamber and inside forms anozzle ejection paddle 213. On the paddle 213 is formed a “poker” 215which is formed when forming the walls of the nozzle chamber 203. Alsoformed on the actuator 206 is a actuator slot protection barrier 216. Anink supply channel 217 is also formed through the surface of thesubstrate 202 utilizing highly anisotropic etching of the substrate 202.During operation, ink flows out of the nozzle chamber 203 so as to forma layer 219 between the slot in the wall 212 and the actuator slotprotection barrier 216. The protection barrier is profiled tosubstantially mate with the slot but to be slightly spaced aparttherefrom so that any meniscus eg. 219 is of small dimensions.

Next, as illustrated in FIG. 2, when it is desired to eject a drop fromthe nozzle chamber 203, the bottom conductive thermal actuator 209 isheated electrically so as to undergo a rapid expansion which in turnresults in the rapid upward movement of the paddle 213. The rapid upwardmovement of the paddle 213 results in ink flow out of the nozzle so asto form bulging ink meniscus 204. Importantly, the movement of theactuator 206 results in the poker 215 moving up through the plane of thenozzle rim so as to assist in the ejection of any debris which may be invicinity of the nozzle rim 205.

Further, the movement of the actuator 206 results in a slight movementof the actuator slot protection barrier 216 which maintainssubstantially the small dimensioned meniscus 219 thereby reducing theopportunity for ink wicking along surfaces. Subsequently, the conductiveheater 209 is turned off and the actuator 206 begins to rapidly returnto its original position. The forward momentum of the ink aroundmeniscus 204 in addition to the backflow due to return movement of theactuator 2026 results in a general necking and breaking of the meniscus204 so as to form a drop.

The situation a short time later is as illustrated in FIG. 3 where adrop 220 proceeds to the print media and the meniscus collapses aroundpoker 215 so as to form menisci 222, 223. The formation of the menisci222, 223 result in a high surface tension pressure being exerted in thenozzle chamber 203 which results in ink being drawn into the nozzlechamber 203 via ink supply channel 217 so as to rapidly refill thenozzle chamber 203. The utilization of the poker 215 increases the speedof refill in addition to ensuring that no air bubble forms within thenozzle chamber 203 by means of the meniscus attaching to the surface ofthe nozzle paddle 213 and remaining there. The poker 215 ensures thatthe meniscus eg. 222, 223 will run along the poker 215 so as to refillin the nozzle chamber. Additionally, the area around the actuator slotbarrier 216 remains substantially stable minimizing the opportunitiesfor wicking therefrom.

Turning now to FIG. 4 there is illustrated a side perspective view of asingle nozzle arrangement 201 shown in sections. FIG. 5 illustrates aside perspective view of a single nozzle including a protective shroud230. The central poker 215 and aperture card 216 are as previouslydiscussed. The construction of the arrangement of FIGS. 4 and 5 can beas a result of the simple modification of deep mask steps utilized inthe construction of the nozzle arrangement in Australian ProvisionalPatent Application PP6534 (the contents of which are specificallyincorporated by cross-reference) so as to include the poker 215 andguard 216. The poker and guard are constructed primarily by means of achemical mechanical planarization step which is illustratedschematically in FIG. 6 to FIG. 8. The poker 215 and guard 216 areconstructed by depositing a surface layer 232 on a sacrificial layer 231which includes a series of etched vias eg. 233. Subsequently, asillustrated in FIG. 7, the top layer is chemically and mechanicallyplanarized off so as to leave the underlying structure 235 which isattached to lower structural layers 236. Subsequently, as illustrated inFIG. 8, the sacrificial layer 231 is etched away leaving the resultingstructure as required.

It would be appreciated by a person skilled in the art that numerousvariations and/or modifications may be made to the present invention asshown in the specific embodiments without departing from the spirit orscope of the invention as broadly described. The present embodimentsare, therefore, to be considered in all respect to be illustrative andnot restrictive.

1. An inkjet printhead comprising: an elongate ink supply channeldefined in a substrate; a plurality of inkjet nozzles arranged on thesubstrate to extend across a pagewidth, each nozzle incorporating: anactuator comprising a conductive heater, a paddle and an arminterconnecting the heater and paddle; and an ink ejection chamberhaving a first wall in which a first aperture for ink ejection isdefined, a second wall in which a second aperture is defined throughwhich the arm of the actuator passes so that the heater is outside thechamber and the paddle is inside the chamber, and a third wall in whicha third aperture is defined through which ink from the ink supplychannel is communicated, wherein the arm of each actuator incorporates aprotruding shield configured to restrict the flow of ink through thesecond aperture.
 2. A printhead as claimed in claim 1, wherein theshield of each actuator arm incorporates a hydrophobic surface.
 3. Aprinthead as claimed in claim 1, wherein the shield of each actuator armis formed on an upper surface of the arm, and, in use, the arm of eachactuator is moved in an upwardly defined direction towards the firstaperture of the associated chamber.
 4. A printhead as claimed in claim1, wherein the actuator comprises thermally expansible material.
 5. Aprinthead as claimed in claim 1, wherein the shield of each actuator armis arranged adjacent the second aperture of the chamber.